View source for Anti-aircraft warfare

{{See also|Surface-to-air missile}}
{{short description|Measures to combat enemy aerial forces}}
{{Redirect-several|dab=no|Flak (disambiguation)|Ack Ack (disambiguation)|Anti-Aircraft (video game)}}
{{Use dmy dates|date=January 2025}}
{{Use British English|date=March 2017}}
[[File:DGLC systemen.jpg|thumb|upright=1.35|Artist's rendition of short and long range AA systems used by the Dutch [[Joint Ground-based Air Defence Command]]]]
{{War}}

'''Anti-aircraft warfare''' is the counter to [[aerial warfare]]<ref>{{cite book |last=Wragg |first=David W. |title=A Dictionary of Aviation |publisher=Osprey |year=1973 |page=37}}</ref> and includes "all measures designed to nullify or reduce the effectiveness of hostile air action".<ref name="AAP-6">AAP-6</ref> It encompasses surface-based, subsurface ([[Submarine#Armament|submarine-launched]]), and air-based weapon systems, in addition to associated sensor systems, command and control arrangements, and passive measures (e.g. [[barrage balloon]]s). It may be used to protect [[naval]], [[army|ground]], and air forces in any location. However, for most countries, the main effort has tended to be [[homeland defence]]. [[Missile defense|Missile defence]] is an extension of air defence, as are initiatives to adapt air defence to the task of intercepting any projectile in flight.

Most modern anti-aircraft (AA) weapons systems are optimized for short-, medium-, or long-range air defence, although some systems may incorporate multiple weapons (such as both [[autocannons]] and [[surface-to-air missiles]]). ‘Layered air defence’ usually refers to multiple ‘tiers’ of air defence systems which, when combined, an airborne threat must penetrate to reach its target; This defence is usually accomplished via the combined use of systems optimized for either short-, medium-, or long-range air defence.

In some countries, such as Britain and Germany during the [[Second World War]], the [[Soviet Union]], and modern NATO and the United States, ground-based air defence and air defence aircraft have been under integrated command and control. However, while overall air defence may be for homeland defence (including military facilities), forces in the field, wherever they are, provide their own defences against airborne threats.

Until the 1950s, guns firing ballistic munitions ranging from 7.62&nbsp;mm (.30 in) to 152.4&nbsp;mm (6&nbsp;in) were the standard weapons; guided missiles then became dominant, except at the very shortest ranges (as with [[close-in weapon system]]s, which typically use [[rotary cannon|rotary autocannon]]s or, in very modern systems, surface-to-air adaptations of short-range [[air-to-air missile]]s, often combined in one system with rotary cannons).

==Terminology==
It may also be called ''counter-air'', ''anti-air'', ''AA'', ''flak'', ''layered air defence'' or ''air defence forces''.

The term ''air defence'' was probably first used by the UK when [[Air Defence of Great Britain]] (ADGB) was created as a [[Royal Air Force]] command in 1925. However, arrangements in the UK were also called ''anti-aircraft'', abbreviated as ''AA'', a term that remained in general use into the 1950s. After the [[First World War]] it was sometimes prefixed by "light" or "heavy" (''LAA'' or ''HAA'') to classify a type of gun or unit. Nicknames for anti-aircraft guns include:

* ''AA'': abbreviations of ''anti-aircraft''
* ''AAA'' or ''triple-A'': abbreviations of ''anti-aircraft artillery''
* ''flak'': from the German ''Flugzeugabwehrkanone'' or ''Fliegerabwehrkanone''
* ''ack-ack'': from the [[spelling alphabet]] used by the British for voice transmission of "AA")<ref>[http://www.oed.com/view/Entry/1600?redirectedFrom=ack-ack "ack-ack, adj. and n.".] {{Webarchive|url=https://web.archive.org/web/20150924085455/http://www.oed.com/view/Entry/1600?redirectedFrom=ack-ack |date=24 September 2015 }} OED Online. September 2013. Oxford University Press. (accessed 14 September 2013).</ref>
* ''archie'': a World War I British term probably coined by [[Amyas Borton]], and believed to derive via the [[Royal Flying Corps]], from the [[music-hall]] comedian [[George Robey]]'s line "Archibald, certainly not!"<ref>{{cite web |url=http://www.rafweb.org/Biographies/Borton.htm |title=Air Vice-Marshal A E Borton |publisher=Rafweb.org |website=Air of Authority – A History of RAF Organisation |archive-url=https://web.archive.org/web/20090303222503/http://www.rafweb.org/Biographies/Borton.htm |archive-date=3 March 2009 |url-status=live }}</ref>

NATO defines anti-aircraft warfare (AAW) as "measures taken to defend a maritime force against attacks by airborne weapons launched from aircraft, ships, submarines and land-based sites".<ref name="AAP-6" /> In some armies the term ''all-arms air defence'' (AAAD) is used for air defence by nonspecialist troops. Other terms from the late 20th century include "ground based air defence" (GBAD) with related terms "[[short range air defense]]" (SHORAD) and [[man-portable air-defense system]] (MANPADS). Anti-aircraft missiles are variously called [[surface-to-air missile]]s, ("SAMs") and surface-to-air guided weapons (SAGWs). Examples are the [[RIM-66 Standard]], [[RIM-174 Standard ERAM|Raytheon Standard Missile 6]], or the [[Aster (missile family)|MBDA Aster]] missile.

Non-English terms for air defence include the German term ''Flak'' or ''FlaK'' (''Fliegerabwehrkanone'', {{Literally|}} 'aircraft defence cannon',<ref>{{cite web |url = http://mw1.merriam-webster.com/dictionary/flak |title = flak |publisher = Merriam-Webster Online Dictionary |access-date = 30 June 2008 |url-status = dead |archive-url = https://web.archive.org/web/20080514025728/http://mw1.merriam-webster.com/dictionary/flak |archive-date = 14 May 2008 |df = dmy-all }}</ref> also cited as ''Flugabwehrkanone''), and the Russian term ''Protivovozdushnaya oborona'' ([[Cyrillic]]: Противовозду́шная оборо́на), {{Literally|}} 'anti-air defence', abbreviated as PVO.{{sfn|Bellamy|1986|p=219}} In Russian, the AA systems are called ''zenitnye'' (i.e., 'pointing to [[zenith]]') systems. In French, air defence is called ''Défense contre les aéronefs (DCA)'' , {{Literally|}} 'defence against aircraft'.<ref>le petit Larousse 2013 p20–p306</ref>

The maximum distance at which a gun or missile can engage an aircraft is an important figure. However, many different definitions are used and unless the same definition is used, performance of different guns or missiles cannot be compared. For AA guns only the ascending part of the trajectory can be usefully used. One term is "ceiling", the maximum ceiling being the height a projectile would reach if fired vertically, not practically useful in itself as few AA guns are able to fire vertically, and the maximum fuse duration may be too short, but potentially useful as a standard to compare different weapons.

The British adopted "effective ceiling", meaning the altitude at which a gun could deliver a series of shells against a moving target; this could be constrained by maximum fuse running time as well as the gun's capability. By the late 1930s the British definition was "that height at which a directly approaching target at {{convert|400 |mph|abbr=on|disp=sqbr}} can be engaged for 20 seconds before the gun reaches 70 degrees elevation".<ref>Hogg WW2 pg 99–100</ref>

== General description ==
[[File:A member of the ATS (Auxiliary Territorial Service) serving with a 3.7-inch anti-aircraft gun battery, December 1942. TR452.jpg|thumb|right|An [[Auxiliary Territorial Service]] spotter with binoculars at an anti-aircraft command post, in front of [[QF 3.7-inch AA gun]] (December 1942).]]
The essence of air defence is to detect hostile aircraft and destroy them. The critical issue is to hit a target moving in three-dimensional space; an attack must not only match these three coordinates, but must do so at the time the target is at that position. This means that projectiles either have to be guided to hit the target, or aimed at the predicted position of the target at the time the projectile reaches it, taking into account the speed and direction of both the target and the projectile.

Throughout the 20th century, air defence was one of the fastest-evolving areas of military technology, responding to the evolution of aircraft and exploiting technology such as radar, guided missiles and computing (initially electromechanical analogue computing from the 1930s on, as with equipment described below). Improvements were made to sensors, technical fire control, weapons, and command and control. At the start of the 20th century these were either very primitive or non-existent.

Initially sensors were optical and acoustic devices developed during World War I and continued into the 1930s,<ref>{{cite magazine|magazine=Popular Mechanics|author=Hearst Magazines|title=Huge Ear Locates Planes and Tells Their Speed|url=https://books.google.com/books?id=qOIDAAAAMBAJ&pg=PA895|date=December 1930|publisher=Hearst Magazines|page=895}}</ref> but were quickly superseded by radar, which in turn was supplemented by [[optoelectronics]] in the 1980s.
Command and control remained primitive until the late 1930s, when Britain created an integrated system<ref>Checkland and Holwell pg. 127</ref> for ADGB that linked the ground-based air defence of the British Army's [[Anti-Aircraft Command]], although field-deployed air defence relied on less sophisticated arrangements. NATO later called these arrangements an "air defence ground environment", defined as "the network of ground radar sites and command and control centres within a specific theatre of operations which are used for the tactical control of air defence operations".<ref name="AAP-6"/>

Rules of engagement are critical to prevent air defences engaging friendly or neutral aircraft. Their use is assisted but not governed by [[identification friend or foe]] (IFF) electronic devices originally introduced during the [[Second World War]]. While these rules originate at the highest authority, different rules can apply to different types of air defence covering the same area at the same time. AAAD usually operates under the tightest rules.

NATO calls these rules "weapon control orders" (WCO), they are:
* ''Weapons free'': weapons may be fired at any target not positively recognised as friendly.
* ''Weapons tight'': weapons may be fired only at targets recognised as hostile.
* ''Weapons hold'': weapons may only be fired in self-defence or in response to a formal order.<ref name="AAP-6"/>

Until the 1950s, guns firing ballistic munitions were the standard weapon; guided missiles then became dominant, except at the very shortest ranges. However, the type of shell or warhead and its fuzing and, with missiles, the guidance arrangement were and are varied. Targets are not always easy to destroy; nonetheless, damaged aircraft may be forced to abort their mission and, even if they manage to return and land in friendly territory, may be out of action for days or permanently. Ignoring small arms and smaller machine-guns, ground-based air defence guns have varied in calibre from 20&nbsp;mm to at least 152&nbsp;mm.{{sfn|Routledge|1994|p=456}}

Ground-based air defence is deployed in several ways:
* Self-defence by ground forces using their organic weapons, AAAD.
* Accompanying defence, specialist air defence elements accompanying armoured or infantry units.
* Point defence around a key target, such as a bridge, critical government building or ship.
* Area air defence, typically "belts" of air defence to provide a barrier, but sometimes an umbrella covering an area. Areas can vary widely in size. They may extend along a nation's border, e.g. the [[Cold War]] [[MIM-23 Hawk]] and [[Nike (rocket)|Nike]] belts that ran north–south across Germany, across a military formation's manoeuvre area, or above a city or port. In ground operations air defence areas may be used offensively by rapid redeployment across current aircraft transit routes.

Air defence has included other elements, although after the Second World War most fell into disuse:
* Tethered [[barrage balloons]] to deter and threaten aircraft flying below the height of the balloons, where they are susceptible to damaging collisions with steel tethers.
* Cables strung across valleys, sometimes forming a "curtain" with vertical cables hanging from them.<ref>{{Cite book |last=Dahl |first=Per F. |url=https://www.worldcat.org/oclc/45728821 |title=Heavy water and the wartime race for nuclear energy |date=1999 |publisher=Institute of Physics |isbn=0-585-25449-4 |location=Bristol [England] |oclc=45728821}}</ref>
* [[Searchlight]]s to illuminate aircraft at night for both gun-layers and optical instrument operators. During World War II searchlights became radar controlled.
* Large [[smoke screen]]s created by large smoke canisters on the ground to screen targets and prevent accurate weapon aiming by aircraft.
Passive air defence is defined by NATO as "Passive measures taken for the physical defence and protection of personnel, essential installations and equipment in order to minimise the effectiveness of air and/or missile attack".<ref name="AAP-6"/> It remains a vital activity by ground forces and includes camouflage and concealment to avoid detection by reconnaissance and attacking aircraft. Measures such as camouflaging important buildings were common in the Second World War. During the Cold War the runways and taxiways of some airfields were painted green.

== Organization ==
While navies are usually responsible for their own air defence—at least for ships at sea—organisational arrangements for land-based air defence vary between nations and over time.

The most extreme case was the Soviet Union and this model may still be followed in some countries: it was a separate service, on a par with the army, navy, or air force. In the Soviet Union, this was called ''[[Soviet Air Defence Forces|Voyska PVO]]'', and had both fighter aircraft, separate from the air force, and ground-based systems. This was divided into two arms, ''PVO Strany,'' the Strategic Air defence Service responsible for Air Defence of the Homeland, created in 1941 and becoming an independent service in 1954, and ''PVO SV,'' Air Defence of the Ground Forces. Subsequently, these became part of the air force and ground forces respectively.{{sfn|Bellamy|1986|p=82}}{{sfn|Bellamy|1986|p=213}}

At the other extreme, the [[United States Army]] has an [[Air Defense Artillery Branch]] that provides ground-based air defence for both homeland and the army in the field; however, it is operationally under the [[Joint Force Air Component Commander]]. Many other nations also deploy an air-defence branch in the army. Some, such as Japan or Israel, choose to integrate their ground based air defence systems into their air force.

In Britain and some other armies, the single artillery branch has been responsible for both home and overseas ground-based air defence, although there was divided responsibility with the [[Royal Navy]] for air defence of the British Isles in [[World War I]]. However, during the [[Second World War]], the [[RAF Regiment]] was formed to protect airfields everywhere, and this included light air defences. In the later decades of the [[Cold War]] this included the [[United States Air Force]]'s operating bases in the UK. All ground-based air defence was removed from Royal Air Force (RAF) jurisdiction in 2004. The British Army's [[Anti-Aircraft Command]] was disbanded in March 1955,<ref>Beckett 2008, 178.</ref> but during the 1960s and 1970s the RAF's Fighter Command operated long-range air-defence missiles to protect key areas in the UK. During World War II, the [[Royal Marines]] also provided air defence units; formally part of the mobile naval base defence organisation, they were handled as an integral part of the army-commanded ground based air defences.

The basic air defence unit is typically a battery with 2 to 12 guns or missile launchers and fire control elements.{{Citation needed|date=February 2024}} These batteries, particularly with guns, usually deploy in a small area, although batteries may be split; this is usual for some missile systems. SHORAD missile batteries often deploy across an area with individual launchers several kilometres apart. When MANPADS is operated by specialists, batteries may have several dozen teams deploying separately in small sections; self-propelled air defence guns may deploy in pairs.

Batteries are usually grouped into battalions or equivalent. In the field army, a light gun or SHORAD battalion is often assigned to a manoeuvre division. Heavier guns and long-range missiles may be in air-defence brigades and come under corps or higher command. Homeland air defence may have a full military structure. For example, the UK's Anti-Aircraft Command, commanded by a full [[Frederick Alfred Pile|British Army general]] was part of ADGB. At its peak in 1941–42 it comprised three AA corps with 12 AA divisions between them.{{sfn|Routledge|1994|p=396–397}}

== History ==

=== Earliest use ===
The use of balloons by the U.S. Army during the American Civil War compelled the Confederates to develop methods of combating them. These included the use of artillery, small arms, and saboteurs. They were unsuccessful, and internal politics led the United States Army's [[Union Army Balloon Corps|Balloon Corps]] to be disbanded mid-war. The Confederates experimented with balloons as well.<ref>Spring 2007 issue of the American Association of Aviation Historians Journal</ref>

Turks carried out the first ever anti-airplane operation in history during the [[Italo-Turkish war]]. Although lacking anti-aircraft weapons, they were the first to shoot down an airplane by rifle fire. The first aircraft to crash in a war was the one of Lieutenant Piero Manzini, shot down on 25 August 1912.<ref>{{Cite web|url=http://www.turkeyswar.com/prelude/turcoitalianwar/|title = Turco-Italian War}}</ref><ref>James D. Crabtree: On air defense, {{ISBN|0275947920}}, Greenwood Publishing Group, page 9</ref>

The earliest known use of weapons specifically made for the anti-aircraft role occurred during the [[Franco-Prussian War]] of 1870. After the [[Battle of Sedan|disaster at Sedan]], [[Siege of Paris (1870–71)|Paris was besieged]] and French troops outside the city started an attempt at communication via [[balloon (aircraft)|balloon]]. Gustav [[Krupp]] mounted a modified 1-pounder (37&nbsp;mm) gun – the ''Ballonabwehrkanone'' (Balloon defence cannon) or ''BaK'' — on top of a horse-drawn carriage for the purpose of shooting down these balloons.<ref>Essential Militaria: Facts, Legends, and Curiosities About Warfare Through the Ages, Nicholas Hobbs, Atlantic Monthly Press 2004, {{ISBN|0-8021-1772-4}}</ref>{{Page needed|date=October 2012}}
<gallery heights="180">
File:Canon antiballons.JPG|''Ballonabwehrkanone'' by Krupp
File:Ballonkanone.JPG|''Ballonabwehrkanone'' by Krupp
File:Balloon gun on Prussian corvette Nymphe 1872 NLV.jpeg|''Ballonabwehrkanone'' on the Prussian corvette [[SMS Nymphe (1863)|Nymphe]] 1872
File:Becker Flab 1917.jpg|20&nbsp;mm Becker-Oerlikon Model 1917 AA-gun 
</gallery>
By the early 20th century balloon, or airship, guns, for land and naval use were attracting attention. Various types of ammunition were proposed, high explosive, incendiary, bullet-chains, rod bullets and shrapnel. The need for some form of tracer or smoke trail was articulated. Fuzing options were also examined, both impact and time types. Mountings were generally pedestal type but could be on field platforms. Trials were underway in most countries in Europe but only Krupp, Erhardt, [[Vickers]] Maxim, and [[Schneider-Creusot|Schneider]] had published any information by 1910. Krupp's designs included adaptations of their 65&nbsp;mm 9-pounder, a 75&nbsp;mm 12-pounder, and even a 105&nbsp;mm gun. Erhardt also had a 12-pounder, while Vickers Maxim offered a 3-pounder and Schneider a 47&nbsp;mm. The French balloon gun appeared in 1910, it was an 11-pounder but mounted on a vehicle, with a total uncrewed weight of two tons. However, since balloons were slow moving, sights were simple. But the challenges of faster moving aeroplanes were recognised.<ref>Bethel pg 56–80</ref>

By 1913 only France and Germany had developed field guns suitable for engaging balloons and aircraft and addressed issues of military organisation. Britain's Royal Navy would soon introduce the [[QF 3-inch 20 cwt|QF 3-inch]] and [[QF 4-inch Mk V naval gun|QF 4-inch]] AA guns and also had [[QF 1-pounder pom-pom|Vickers 1-pounder quick firing "pom-poms"]] that could be used in various mountings.{{sfn|Routledge|1994|p=3}}{{sfn|Routledge|1994|p=4}}

The first US anti-aircraft cannon was a 1-pounder concept design by [[Nathan Crook Twining|Admiral Twining]] in 1911 to meet the perceived threat of airships, that eventually was used as the basis for the US Navy's first operational anti-aircraft cannon: the [[3"/23 caliber gun|3-inch/23 caliber gun]].<ref>{{cite magazine|magazine=Popular Mechanics|author=Hearst Magazines|title=New American Aerial Weapons|url=https://books.google.com/books?id=-t0DAAAAMBAJ&pg=PA776|date=December 1911|publisher=Hearst Magazines|page=776}}</ref>

=== First World War ===
[[File:Krupps 9 pounder 1909.jpg|thumb|1909 vintage Krupp 9-pounder anti-aircraft gun]]
[[File:Canadian 1918 antiaircraft team.jpg|thumb|A Canadian anti-aircraft unit of 1918 "taking post"]]
[[File:Anti-aircraft motor battery against Zeppelin in Horseless Age v37 n7 p261.png|thumb|upright|A French anti-aircraft motor battery (motorized AAA battery) that brought down a [[Zeppelin]] near Paris. From the journal ''Horseless Age'', 1916.]]

On 30 September 1915, troops of the [[Serbian Army]] observed three enemy aircraft approaching [[Kragujevac]]. Soldiers fired at them with shotguns and machine-guns but failed to prevent them from dropping 45 bombs over the city, hitting military installations, the railway station and many other, mostly civilian, targets in the city. During the bombing raid, private [[Radoje Ljutovac]] fired his cannon at the enemy aircraft and successfully shot one down. It crashed in the city and both pilots died from their injuries. The cannon Ljutovac used was not designed as an anti-aircraft gun; it was a slightly modified Turkish cannon captured during the [[First Balkan War]] in 1912. This was the first occasion in military history that a military aircraft was shot down with [[ground-to-air]] artillery fire.<ref>{{cite magazine| url=http://www.nationalgeographic.rs/vesti/3842-prvi-ratni-avion-oboren-u-istoriji-pao-na-kragujevac.html| title=How was the first military airplane shot down| magazine=National Geographic| access-date=5 August 2015| archive-url=https://web.archive.org/web/20150831011608/http://www.nationalgeographic.rs/vesti/3842-prvi-ratni-avion-oboren-u-istoriji-pao-na-kragujevac.html| archive-date=31 August 2015| url-status=live}}</ref><ref>{{cite web|url=http://www.thefirstworldwar.net/licnosti/ucesnici-ratova/ljutovac-radoje/ |title=Ljutovac, Radoje |publisher=Amanet Society |access-date=5 August 2015 |url-status=dead |archive-url=https://web.archive.org/web/20141006071649/http://www.thefirstworldwar.net/licnosti/ucesnici-ratova/ljutovac-radoje/ |archive-date=6 October 2014 }}</ref><ref>{{cite web|url=http://www.pecat.co.rs/2014/09/radoje-raka-ljutovac-prvi-u-svetu-oborio-avion-topom/|title=Radoje Raka Ljutovac – first person in the world to shoot down an airplane with a cannon|date=30 September 2014|publisher=Pečat|access-date=5 August 2015|archive-url=https://web.archive.org/web/20150812103535/http://www.pecat.co.rs/2014/09/radoje-raka-ljutovac-prvi-u-svetu-oborio-avion-topom/|archive-date=12 August 2015|url-status=live}}</ref>

The British recognised the need for anti-aircraft capability a few weeks before World War I broke out; on 8 July 1914, the ''New York Times'' reported that the British government had decided to "dot the coasts of the British Isles with a series of towers, each armed with two quick-firing guns of special design," while "a complete circle of towers" was to be built around "naval installations" and "at other especially vulnerable points". By December 1914 the [[Royal Naval Volunteer Reserve]] (RNVR) was manning AA guns and searchlights assembled from various sources at some nine ports. The [[Royal Garrison Artillery]] (RGA) was given responsibility for AA defence in the field, using motorised two-gun sections. The first were formally formed in November 1914. Initially they used [[QF 1-pounder pom-pom|QF 1-pounder "pom-pom"]]s (37&nbsp;mm versions of the [[Maxim Gun]]).{{sfn|Routledge|1994|p=4}}{{sfn|Routledge|1994|p=5}}
[[File:Maxim anti-aircraft machine gun.JPG|thumb|upright|A Maxim anti-aircraft machine gun in the anti-aircraft museum in Finland, 2006]]

All armies soon deployed AA guns often based on their smaller field pieces, notably the French 75&nbsp;mm and Russian 76.2&nbsp;mm, typically simply propped up on some sort of embankment to get the muzzle pointed skyward. The [[British Army]] adopted the 13-pounder quickly producing new mountings suitable for AA use, the [[QF 13-pounder 6 cwt AA gun|13-pdr QF 6&nbsp;cwt Mk III]] was issued in 1915. It remained in service throughout the war but 18-pdr guns were lined down to take the 13-pdr shell with a larger cartridge producing the [[QF 13-pounder 9 cwt|13-pr QF 9&nbsp;cwt]] and these proved much more satisfactory.{{sfn|Routledge|1994|p=6}} However, in general, these ad hoc solutions proved largely useless. With little experience in the role, no means of measuring target, range, height or speed the difficulty of observing their shell bursts relative to the target gunners proved unable to get their fuse setting correct and most rounds burst well below their targets. The exception to this rule was the guns protecting spotting balloons, in which case the altitude could be accurately measured from the length of the cable holding the balloon.

The first issue was ammunition. Before the war it was recognised that ammunition needed to explode in the air. Both high explosive (HE) and [[Shrapnel shell|shrapnel]] were used, mostly the former. Airburst fuses were either igniferious (based on a burning fuse) or mechanical (clockwork). Igniferious fuses were not well suited for anti-aircraft use. The fuse length was determined by time of flight, but the burning rate of the gunpowder was affected by altitude. The British pom-poms had only contact-fused ammunition. [[Zeppelin]]s, being hydrogen-filled balloons, were targets for incendiary shells and the British introduced these with airburst fuses, both shrapnel type-forward projection of incendiary "pot" and base ejection of an incendiary stream. The British also fitted tracers to their shells for use at night. Smoke shells were also available for some AA guns, these bursts were used as targets during training.<ref>The Ministry of Munitions pg 40–41</ref>

German air attacks on the British Isles increased in 1915 and the AA efforts were deemed somewhat ineffective, so a [[Royal Navy]] gunnery expert, Admiral Sir [[Percy Scott]], was appointed to make improvements, particularly an integrated AA defence for London. The air defences were expanded with more RNVR AA guns, 75&nbsp;mm and 3-inch, the pom-poms being ineffective. The naval 3-inch was also adopted by the army, the [[QF 3-inch 20 cwt]] (76&nbsp;mm), a new field mounting was introduced in 1916. Since most attacks were at night, searchlights were soon used, and acoustic methods of detection and locating were developed. By December 1916 there were 183 AA sections defending Britain (most with the 3-inch), 74 with the BEF in France and 10 in the Middle East.{{sfn|Routledge|1994|p=8–17}}

AA gunnery was a difficult business. The problem was of successfully aiming a shell to burst close to its target's future position, with various factors affecting the shells' predicted trajectory. This was called deflection gun-laying, where "off-set" angles for range and elevation were set on the gunsight and updated as their target moved. In this method, when the sights were on the target, the barrel was pointed at the target's future position. Range and height of the target determined fuse length. The difficulties increased as aircraft performance improved.

The British dealt with range measurement first, when it was realised that range was the key to producing a better fuse setting. This led to the [[Height finder#Optical|height/range finder]] (HRF), the first model being the [[Barr & Stroud]] UB2, a two-metre [[Coincidence rangefinder|optical coincident rangefinder]] mounted on a tripod. It measured the distance to the target and the elevation angle, which together gave the height of the aircraft. These were complex instruments and various other methods were also used. The HRF was soon joined by the height/fuse indicator (HFI), this was marked with elevation angles and height lines overlaid with fuse length curves, using the height reported by the HRF operator, the necessary fuse length could be read off.{{sfn|Routledge|1994|p=14–15}}

However, the problem of deflection settings — "aim-off" — required knowing the rate of change in the target's position. Both France and the UK introduced tachymetric devices to track targets and produce vertical and horizontal deflection angles. The French Brocq system was electrical; the operator entered the target range and had displays at guns; it was used with their 75&nbsp;mm. The British Wilson-Dalby gun director used a pair of trackers and mechanical tachymetry; the operator entered the fuse length, and deflection angles were read from the instruments.{{sfn|Routledge|1994|p=14–20}}<ref>The Ministry of Munitions pg 11</ref>

By the start of [[World War I]], the 77&nbsp;mm had become the standard German weapon, and came mounted on a large traverse that could be easily transported on a wagon. Krupp 75&nbsp;mm guns were supplied with an optical sighting system that improved their capabilities. The German Army also adapted a revolving cannon that came to be known to Allied fliers as the "[[flaming onion]]" from the shells in flight. This gun had five barrels that quickly launched a series of 37&nbsp;mm artillery shells.{{citation needed|date=October 2020}}

As aircraft started to be used against ground targets on the battlefield, the AA guns could not be traversed quickly enough at close targets and, being relatively few, were not always in the right place (and were often unpopular with other troops), so changed positions frequently. Soon the forces were adding various machine-gun based weapons mounted on poles. These short-range weapons proved more deadly, and the "[[Manfred von Richthofen|Red Baron]]" is believed to have been shot down by an anti-aircraft [[Vickers machine gun]]. When the war ended, it was clear that the increasing capabilities of aircraft would require better means of acquiring targets and aiming at them. Nevertheless, a pattern had been set: anti-aircraft warfare would employ heavy weapons to attack high-altitude targets and lighter weapons for use when aircraft came to lower altitudes.

[[File:AA-Predictor-Nr1MarkIII-001.jpg|thumb|The No. 1 Mark III Predictor that was used with the [[QF 3.7-inch AA gun]] was a mechanical computer.]]
[[File:Antiaircraft defence Sweden 1934.jpg|thumb|Shooting with anti-aircraft gun in Sweden 1934]]

=== Interwar years ===
World War I demonstrated that aircraft could be an important part of the battlefield, but in some nations it was the prospect of strategic air attack that was the main issue, presenting both a threat and an opportunity. The experience of four years of air attacks on London by Zeppelins and [[Gotha G.V]] bombers had particularly influenced the British and was one of if not the main driver for forming an independent air force. As the capabilities of aircraft and their engines improved it was clear that their role in future war would be even more critical as their range and weapon load grew. However, in the years immediately after World War I, the prospect of another major war seemed remote, particularly in Europe, where the most militarily capable nations were, and little financing was available.

Four years of war had seen the creation of a new and technically demanding branch of military activity. Air defence had made huge advances, albeit from a very low starting point. However, it was new and often lacked influential 'friends' in the competition for a share of limited defence budgets. Demobilisation meant that most AA guns were taken out of service, leaving only the most modern.

However, there were lessons to be learned. In particular the British, who had had AA guns in most theatres in action in daylight and used them against night attacks at home. Furthermore, they had also formed an [[Anti-Aircraft Experimental Section]] during the war and accumulated large amounts of data that was subjected to extensive analysis. As a result, they published the two-volume ''Textbook of Anti-Aircraft Gunnery''  in 1924–1925. It included five key recommendations for HAA equipment:
* Shells of improved ballistic shape with HE fillings and mechanical time fuses
* Higher rates of fire assisted by automation
* Height finding by long-base optical instruments
* Centralised control of fire on each gun position, directed by tachymetric instruments incorporating the facility to apply corrections of the moment for meteorological and wear factors
* More accurate sound-location for the direction of searchlights and to provide plots for barrage fire
Two assumptions underpinned the British approach to HAA fire; first, aimed fire was the primary method and this was enabled by predicting gun data from visually tracking the target and having its height. Second, that the target would maintain a steady course, speed and height. This HAA was to engage targets up to {{Convert|24,000|ft|km|abbr=on}}. Mechanical time fuses were required because the speed of powder burning varied with height, so fuse length was not a simple function of time of flight. Automated fire ensured a constant rate of fire that made it easier to predict where each shell should be individually aimed.{{sfn|Routledge|1994|p=48}}{{sfn|Routledge|1994|p=49}}

In 1925 the British adopted a new instrument developed by Vickers. It was a mechanical [[Analog computer|analogue computer]] – the Predictor AA No 1. Given the target height, its operators tracked the target and the predictor produced bearing, quadrant elevation and fuse setting. These were passed electrically to the guns, where they were displayed on repeater dials to the layers who "matched pointers" (target data and the gun's actual data) to lay the guns. This system of repeater electrical dials built on the arrangements introduced by British coast artillery in the 1880s, and coast artillery was the background of many AA officers. Similar systems were adopted in other countries and for example the later Sperry M3A3 in the US, was also used by Britain as the Predictor AA No 2. Height finders were also increasing in size; in Britain, the {{cvt|7|ft}} optical base World War I [[Barr & Stroud]] UB 2 [[stereoscopic rangefinder]] was replaced by the {{cvt|9|ft}} optical base UB 7  and the {{cvt|18|ft}} base UB 10 (only used on static AA sites). Goertz in Germany and Levallois in France produced {{Convert|5|metre|ft|0|adj=on|spell=in}} instruments. However, in most countries the main effort in HAA guns until the mid-1930s was improving existing ones, although various new designs were on drawing boards.{{sfn|Routledge|1994|p=49}}{{sfn|Routledge|1994|p=50}}

From the early 1930s eight countries [[History of radar|developed radar]]; these developments were sufficiently advanced by the late 1930s for development work on [[acoustic location|sound-locating acoustic devices]] to be generally halted, although equipment was retained. Furthermore, in Britain the volunteer [[Royal Observer Corps|Observer Corps]] formed in 1925 provided a network of observation posts to report hostile aircraft flying over Britain. Initially radar was used for airspace surveillance to detect approaching hostile aircraft. However, the German [[Würzburg radar]] put into use in 1940 was capable of providing data suitable for controlling AA guns, and the British  [[GL Mk. I radar|Radar, Gun Laying, Mark I]], was designed to be used on AA gun positions and was in use by 1939.{{sfn|Routledge|1994|p=95-97}}

The [[Treaty of Versailles]] prevented Germany having AA weapons, and for example, the Krupps designers joined Bofors in Sweden. Some World War I guns were retained and some covert AA training started in the late 1920s. Germany introduced the 8.8&nbsp;cm FlaK 18 in 1933, the 36 and 37 models followed with various improvements, but ballistic performance was unchanged. In the late 1930s the [[10.5 cm FlaK 38|10.5&nbsp;cm FlaK 38]] appeared, soon followed by the 39; this was designed primarily for static sites but had a mobile mounting, and the unit had 220&nbsp;V 24&nbsp;kW generators. In 1938 design started on the [[12.8 cm FlaK 40|12.8&nbsp;cm FlaK]].{{sfn|Hogg|1997|p=14}}{{sfn|Hogg|1997|p=162–177}}

Britain had successfully tested a new 3.6-inch gun, in 1918. In 1928 a {{Convert|3.7|in|mm|abbr=out|adj=on}} gun became the preferred solution, but it took six years to gain funding. Production of the [[QF 3.7-inch AA gun|QF 3.7-inch gun]]  began in 1937; this gun was used on mobile carriages with the field army and transportable guns on fixed mountings for static positions. At the same time the Royal Navy adopted a new [[QF 4.5-inch Mk I – V naval gun|4.5-inch (113&nbsp;mm) gun]] in a twin turret, which the army adopted in simplified single-gun mountings for static positions, mostly around ports where naval ammunition was available. The performance of the new guns was limited by their standard fuse No 199, with a 30-second running time, although a new mechanical time fuse giving 43 seconds was nearing readiness. In 1939 a machine fuse setter was introduced to eliminate manual fuse setting.<ref>Hogg Allied WW2 pg 97–107</ref>

The US ended World War I with two 3-inch AA guns and improvements were developed throughout the inter-war period. However, in 1924 work started on a new 105&nbsp;mm static mounting AA gun, but only a few were produced by the mid-1930s because by this time work had started on the 90&nbsp;mm AA gun, with mobile carriages and static mountings able to engage air, sea and ground targets. The M1 version was approved in 1940. During the 1920s there was some work on a 4.7-inch which lapsed, but revived in 1937, leading to a new gun in 1944.<ref>Hogg Allied WW2 pg 114–119</ref>

While HAA and its associated target acquisition and fire control was the primary focus of AA efforts, low-level close-range targets remained and by the mid-1930s were becoming an issue.

Until this time the British, at RAF insistence, continued their use of World War I machine guns, and introduced twin MG mountings for AAAD. The army was forbidden from considering anything larger than .50-inch.{{Citation needed|date=February 2024}} However, in 1935 their trials showed that the minimum effective round was an impact-fused 2&nbsp;lb HE shell. The following year they decided to adopt the [[Bofors 40 mm L/60 gun|Bofors 40&nbsp;mm]] and a [[QF 2-pounder naval gun|twin barrel Vickers 2-pdr]] (40&nbsp;mm) on a modified naval mount. The air-cooled Bofors was vastly superior for land use, being much lighter than the water-cooled "pom-pom", and UK production of the Bofors 40&nbsp;mm was licensed. The Predictor AA No 3, as the [[Kerrison Predictor]] was officially known, was introduced with it.<ref>Hogg Allied WW2 pg 108–110</ref>

The 40&nbsp;mm Bofors had become available in 1931. In the late 1920s the [[Swedish Navy]] had ordered the development of a 40&nbsp;mm naval anti-aircraft gun from the Bofors company. It was light, rapid-firing and reliable, and a mobile version on a four-wheel carriage was soon developed. Known simply as the [[Bofors 40 mm Automatic Gun L/60|40 mm]], it was adopted by some 17 different nations just before World War II and is still in use today in some applications such as on coastguard frigates.

Rheinmetall in Germany developed an automatic 20&nbsp;mm in the 1920s and Oerlikon in Switzerland had acquired the patent to an automatic 20&nbsp;mm gun designed in Germany during World War I. Germany introduced the rapid-fire [[2 cm Flak 30, Flak 38 and Flakvierling 38|2&nbsp;cm FlaK 30]] and later in the decade it was redesigned by Mauser-Werke and became the 2&nbsp;cm FlaK 38.{{sfn|Hogg|1997|p=144–147}} Nevertheless, while 20&nbsp;mm was better than a machine gun and mounted on a very small trailer made it easy to move, its effectiveness was limited. Germany therefore added a 3.7&nbsp;cm. The first, the [[3.7 cm Flak 18/36/37|3.7&nbsp;cm FlaK 18]] developed by Rheinmetall in the early 1930s, was basically an enlarged 2&nbsp;cm FlaK 30. It was introduced in 1935 and production stopped the following year. A redesigned gun 3.7&nbsp;cm FlaK 36 entered service in 1938, it too had a two-wheel carriage.{{sfn|Hogg|1997|p=150–152}} However, by the mid-1930s the Luftwaffe realised that there was still a coverage gap between 3.7&nbsp;cm and 8.8&nbsp;cm guns. They started development of a 5&nbsp;cm gun on a four-wheel carriage.{{sfn|Hogg|1997|p=155–156}}

After World War I the US Army started developing a dual-role (AA/ground) automatic 37&nbsp;mm cannon, designed by [[John Browning|John M. Browning]]. It was standardised in 1927 as the T9 AA cannon, but trials quickly revealed that it was worthless in the ground role. However, while the shell was a bit light (well under 2&nbsp;lbs) it had a good effective ceiling and fired 125 rounds per minute; an AA carriage was developed and it entered service in 1939 as the [[37 mm gun M1]]. It proved prone to jamming, and was eventually replaced in AA units by the Bofors 40&nbsp;mm. The Bofors had attracted attention from the US Navy, but none were acquired before 1939.<ref>Hogg Allied WW2 pg 115–117</ref> Also, in 1931 the US Army worked on a mobile anti-aircraft machine mount on the back of a heavy truck having four .30 calibre water-cooled machine guns and an optical director. It proved unsuccessful and was abandoned.<ref>{{cite magazine|magazine=Popular Mechanics|author=Hearst Magazines|title=Uncle Sam's Latest Weapons For War in the Air|url=https://books.google.com/books?id=0-IDAAAAMBAJ&pg=PA944|date=December 1931|publisher=Hearst Magazines|page=944}}</ref>

The USSR introduced a new 76&nbsp;mm ''M1931'' in 1937, an 85&nbsp;mm ''M1938''<ref>Hogg Allied WW2 pg 127–130</ref> and developed the [[37 mm automatic air defense gun M1939 (61-K)|37&nbsp;mm M1939 (61-K)]], which appears to have been copied from the Bofors 40&nbsp;mm. A Bofors 25&nbsp;mm, essentially a scaled down 40&nbsp;mm, was also copied as the [[25 mm automatic air defense gun M1940 (72-K)|25&nbsp;mm M1939]].<ref>Hogg Allied WW2 pg 131</ref>

During the 1930s solid-fuel rockets were under development in the Soviet Union and Britain. In Britain the interest was for anti-aircraft fire, it quickly became clear that guidance would be required for precision. However, rockets, or "[[Unrotated Projectile]]s" as they were called, could be used for anti-aircraft barrages. A two-inch rocket using HE or wire obstacle warheads – the [[Z Battery]] – was introduced first to deal with low-level or dive bombing attacks on smaller targets such as airfields. The three-inch was in development at the end of the inter-war period.{{sfn|Routledge|1994|p=56}}

==== Naval aspects ====

WWI had been a war in which air warfare blossomed, but had not matured to the point of being a real threat to naval forces.  The prevailing assumption was that a few relatively small caliber naval guns could manage to keep enemy aircraft beyond a range where harm might be expected. In 1939 radio controlled [[target drone]]s became available to the US Navy in quantity allowing a more realistic testing of existing anti-aircraft suites against actual flying and manoeuvring targets.<ref name="ReferenceA">Friedman, Norman Naval Anti-Aircraft Guns and Gunnery Location 242</ref> The results were sobering to an unexpected degree.

The United States was still emerging from the effects of the [[Great Depression]] and funds for the military had been sparse to the degree that 50% of shells used were still powder fused.<ref name="ReferenceA"/> The US Navy found that a significant portion of its shells were duds or low order detonations (incomplete detonation of the explosive contained by the shell). Virtually every major country involved in combat in World War II invested in aircraft development. The cost of aircraft research and development was small and the results could be large.<ref>Friedman, Norman Naval Anti-Aircraft Guns and Gunnery Location 266</ref> So rapid was the performance leaps of evolving aircraft that the British [[HACS|High Angle Control System]] (HACS) was obsolete and designing a successor very difficult for the British establishment.<ref name="ReferenceB">Friedman, Norman Naval Anti-Aircraft Guns and Gunnery Location 271</ref> Electronics would prove to be an enabler for effective anti-aircraft systems and both the US and UK had a growing electronics industry.<ref name="ReferenceB"/>

In 1939 radio controlled drones became available to actually test existing systems in British and American service. The results were disappointing by any measure. High-level manoeuvring drones were virtually immune to shipboard AA systems. The US drones could simulate dive bombing which showed the dire need for autocannons. Japan introduced powered gliders in 1940 as drones but apparently was unable to dive bomb.<ref>Friedman, Norman Naval Anti-Aircraft Guns and Gunnery Location 1617</ref> There is no evidence of other powers using drones in this application at all. It may have caused a major underestimation of the threat and an inflated view of their AA systems.<ref>Friedman, Norman Naval Anti-Aircraft Guns and Gunnery Location 1642</ref>

=== Second World War ===
{{more citations needed section|date=July 2013}}

Poland's AA defences were no match for the German attack, and the situation was similar in other European countries.<ref>{{Cite web |title=The Battle of Britain |url=https://www.raf100schools.org.uk/files/download/61/1516097436 |url-status=live |archive-url=https://web.archive.org/web/20180917182108/https://www.raf100schools.org.uk/files/download/61/1516097436 |archive-date=17 September 2018 |website=raf100schools.org.uk}}</ref> Significant AAW (Anti-Air Warfare) started with the [[Battle of Britain]] in the summer of 1940. [[QF 3.7-inch AA gun]]s provided the backbone of the ground-based AA defences, although initially significant numbers of [[QF 3-inch 20 cwt]] were also used. The Army's Anti-aircraft command, which was under operational command of [[RAF Fighter Command]] within Air Defence GB, grew to 12 AA divisions in three AA corps. [[Bofors 40 mm Automatic Gun L/60|Bofors 40 mm gun]]s entered service in increasing numbers. In addition, the RAF regiment was formed in 1941 with responsibility for airfield air defence, eventually with Bofors 40&nbsp;mm as their main armament. Fixed AA defences, using HAA and LAA, were established by the Army in key overseas places, notably [[Malta]], [[Suez Canal]] and [[Singapore in the Straits Settlements|Singapore]].

While the 3.7-inch was the main HAA gun in fixed defences and the only mobile HAA gun with the field army, the [[QF 4.5-inch Mk I – V naval gun|QF 4.5-inch gun]], manned by artillery, was used in the vicinity of naval ports and made use of the naval ammunition supply. The 4.5-inch at Singapore had the first success in shooting down Japanese bombers. Mid war [[QF 5.25-inch naval gun]]s started being emplaced in some permanent sites around London. This gun was also deployed in dual-role coast defence/AA positions.

[[File:Bundesarchiv Bild 101I-635-3999-24, Deutschland, Flak-Batterie in Feuerstellung.jpg|thumb|upright|German [[8.8&nbsp;cm Flak 18/36/37/41|88 mm]] flak gun in action against Allied bombers]]

Germany's high-altitude needs were originally going to be filled by a 75&nbsp;mm gun from [[Krupp]], designed in collaboration with their Swedish counterpart [[Bofors]], but the specifications were later amended to require much higher performance. In response Krupp's engineers presented a new 88&nbsp;mm design, the [[88 mm gun|FlaK 36]]. First used in Spain during the [[Spanish Civil War]], the gun proved to be one of the best anti-aircraft guns in the world, as well as particularly deadly against light, medium, and even early heavy tanks.

After the [[Operation Chastise|Dambusters raid]] in 1943 an entirely new system was developed that was required to knock down any low-flying aircraft with a single hit. The first attempt to produce such a system used a 50&nbsp;mm gun, but this proved inaccurate and a new 55&nbsp;mm gun replaced it. The system used a centralised control system including both search and targeting [[radar]], which calculated the aim point for the guns after considering windage and ballistics, and then sent electrical commands to the guns, which used [[hydraulic]]s to point themselves at high speeds. Operators simply fed the guns and selected the targets. This system, modern even by today's standards, was in late development when the war ended.

[[File:Wehrmacht Flugabwehr Airdefence.jpeg|thumb|upright|German soldier manning an [[MG 34|MG34]] anti-aircraft gun in WWII]]

The British had already arranged licence building of the Bofors 40&nbsp;mm, and introduced these into service. These had the power to knock down aircraft of any size, yet were light enough to be mobile and easily swung. The gun became so important to the British war effort that they even produced a movie, ''[[The Gun (1940 film)|The Gun]]'', that encouraged workers on the assembly line to work harder. The Imperial measurement production drawings the British had developed were supplied to the Americans who produced their own (unlicensed) copy of the 40&nbsp;mm at the start of the war, moving to licensed production in mid-1941.

[[File:B-24 hit by Flak.jpg|thumb|left|A [[USAAF]] [[Consolidated B-24 Liberator]] hit by flak over Italy, 10 April 1945]]

Service trials demonstrated another problem however: that ranging and tracking the new high-speed targets was almost impossible. At short range, the apparent target area is relatively large, the trajectory is flat and the time of flight is short, allowing to correct lead by watching the tracers. At long range, the aircraft remains in firing range for a long time, so the necessary calculations can, in theory, be done by slide rules—though, because small errors in distance cause large errors in shell fall height and detonation time, exact ranging is crucial. For the ranges and speeds that the Bofors worked at, neither answer was good enough.

[[File:Hyde Park Anti-aircraft guns H 993.jpg|thumb|right|British [[QF 3.7-inch AA|QF 3.7-inch]] gun in London in 1939]]

The solution was [[automation]], in the form of a mechanical computer, the [[Kerrison Predictor]]. Operators kept it pointed at the target, and the Predictor then calculated the proper aim point automatically and displayed it as a pointer mounted on the gun. The gun operators simply followed the pointer and loaded the shells. The Kerrison was fairly simple, but it pointed the way to future generations that incorporated radar, first for ranging and later for tracking. Similar predictor systems were introduced by Germany during the war, also adding radar ranging as the war progressed.

[[File:20-mm-AA-cannon.gif|thumb|left|US coast guardsmen in the South Pacific man a 20&nbsp;mm anti-aircraft cannon]]

A plethora of anti-aircraft gun systems of smaller calibre was available to the German Wehrmacht combined forces, and among them the 1940-origin [[2 cm Flak 30/38/Flakvierling#2 cm Flakvierling 38|'' Flakvierling'']] quadruple-20&nbsp;mm-[[autocannon]]-based anti-aircraft weapon system was one of the most often-seen weapons, seeing service on both land and sea. The similar [[Allies of World War II|Allied]] smaller-calibre air-defence weapons of the American forces were also quite capable. Their needs could cogently be met with smaller-calibre ordnance beyond using the usual singly-mounted [[M2 Browning machine gun|M2]] [[.50 BMG|.50 caliber]] machine gun atop a tank's turret, as four of the ground-used "heavy barrel" (M2HB) guns were mounted together on the American Maxson [[M45 Quadmount]] weapon (as a direct answer to the ''Flakvierling''), which were often mounted on the back of a [[half-track]] to form the [[M16 Multiple Gun Motor Carriage]]. Although of less power than Germany's 20&nbsp;mm systems, the typical four or five combat batteries of an Army AAA battalion were often spread many kilometres apart from each other, rapidly attaching and detaching to larger ground combat units to provide welcome defence from enemy aircraft.

[[File: Anti-aircraft BrenGun.jpg|thumb|Indian troops manning a [[Bren light machine gun]] in an anti-aircraft mount in 1941]]

AAA battalions were also used to help suppress ground targets. Their larger [[90 mm M3 gun]] would prove, as did the eighty-eight, to make an excellent anti-tank gun as well, and was widely used late in the war in this role. Also available to the Americans at the start of the war was the [[120 mm M1 gun]] ''stratosphere gun'', which was the most powerful AA gun with an impressive {{convert|60000|ft|km|abbr=on}} altitude capability, however no 120 M1 was ever fired at an enemy aircraft. The 90&nbsp;mm and 120&nbsp;mm guns continued to be used into the 1950s.

The [[United States Navy]] had also put some thought into the problem, When the US Navy began to rearm in 1939 in many ships the primary short ranged gun was the M2 .50 caliber machine gun. While effective in fighters at 300 to 400 yards this is point blank range in naval anti-aircraft ranges. Production of the Swiss Oerlikon 20&nbsp;mm had already started to provide protection for the British and this was adopted in exchange for the M2 machine guns.<ref>Friedman, 2014 Location 8687</ref> From December 1941 to January 1942, production had risen to not only cover all British requirements but also allowed 812 units to be actually delivered to the US Navy.<ref>Friedman, 2014 Location 8713</ref> By the end of 1942 the 20&nbsp;mm had accounted for 42% of all aircraft destroyed by the US Navy's shipboard AA. However, the King Board had noted that the balance was shifting towards the larger guns used by the fleet. The US Navy had intended to use the British pom-pom, however, the weapon required the use of cordite which BuOrd had found objectionable for US service.<ref>Bulletin of Ordnance Information, No.245, pp. 54–60.</ref> Further investigation revealed that US powders would not work in the pom-pom.<ref>Friedman, 2014 Location 8620</ref> Bureau of Ordnance was well aware of the Bofors 40&nbsp;mm gun. The firm York Safe and Lock was negotiating with Bofors to attain the rights to the air-cooled version of the weapon. At the same time Henry Howard, an engineer, and businessman became aware of it and contacted RADM W. R. Furlong, chief of the Bureau of Ordnance. He ordered the Bofors weapon system to be investigated. York Safe and Lock would be used as the contracting agent. The system had to be redesigned for both the English measurement system and mass production, as the original documents recommended hand fitting parts and drilling to shape.<ref>Friedman, 2014 Location 8956-8620</ref> As early as 1928 the US Navy saw the need to replace the .50 caliber machine gun with something heavier. The 1.1"/75 (28&nbsp;mm) Mark 1 was designed. Placed in quadruple mounts with a 500 rpm rate of fire it would have fit the requirements. However, the gun was suffering teething issues being prone to jamming. While this could have been solved the weight of the system was equal to that of the quad-mount Bofors 40&nbsp;mm while lacking the range and power that the Bofors provided. The gun was relegated to smaller less vital ships by the end of the war.<ref>{{Cite web |url=http://www.navweaps.com/Weapons/WNUS_1-1-75_mk1.php |title=USA 1.1"/75 (28 mm) Mark 1 and Mark 2 – NavWeaps |access-date=2 March 2019 |archive-url=https://web.archive.org/web/20180930212147/http://www.navweaps.com/Weapons/WNUS_1-1-75_mk1.php |archive-date=30 September 2018 |url-status=live }}</ref> The [[5-inch/38-caliber gun|5"/38 naval gun]] rounded out the US Navy's AA suite. A dual purpose mount, it was used in both the surface and AA roles with great success. 
Mated with the Mark 37 director and the proximity fuse it could routinely knock drones out of the sky at ranges as far as 13,000 yards.<ref>{{Cite web |url=http://www.navweaps.com/Weapons/WNUS_5-38_mk12.php |title=USA 5"/38 (12.7 cm) Mark 12 – NavWeaps |access-date=2 March 2019 |archive-url=https://web.archive.org/web/20170928150652/http://www.navweaps.com/Weapons/WNUS_5-38_mk12.php |archive-date=28 September 2017 |url-status=live }}</ref>[[File:USS New Mexico Flak Kamikaze Battle of Okinawa.jpg|thumb|right|[[5-inch/38-caliber gun|5-inch]], [[Bofors 40 mm L/60 gun|40&nbsp;mm]] and [[Oerlikon 20 mm cannon|20&nbsp;mm]] fire directed from [[USS New Mexico (BB-40)|USS ''New Mexico'']] at a [[Kamikaze]], [[Battle of Okinawa]], 1945]]A 3"/50 MK 22 semiautomatic dual gun was produced but not employed before the end of the war and therefore beyond the scope of this article. However early marks of the 3"/50 were employed in destroyer escorts and on merchant ships. 3″/50 [[Caliber (artillery)|caliber]] guns (Marks 10, 17, 18, and 20) first entered service in 1915 as a refit to {{USS|Texas|BB-35}}, and were subsequently mounted on many types of ships as the need for anti-aircraft protection was recognized. During World War II, they were the primary gun armament on [[destroyer escort]]s, [[patrol frigate]]s, [[submarine chaser]]s, [[minesweeper (ship)|minesweeper]]s, some fleet [[submarine]]s, and other auxiliary vessels, and were used as a secondary dual-purpose battery on some other types of ships, including some older battleships. They also replaced the original low-angle [[4"/50 caliber gun]]s (Mark 9) on "flush-deck" {{sclass|Wickes|destroyer|5}} and {{sclass|Clemson|destroyer|1}}s to provide better anti-aircraft protection. The gun was also used on specialist destroyer conversions; the "AVD" [[seaplane tender]] conversions received two guns; the "APD" [[high-speed transport]]s, "DM" [[minelayer]]s, and [[Destroyer minesweeper|"DMS" minesweeper]] conversions received three guns, and those retaining destroyer classification received six.<ref>Silverstone 1968 pp. 112, 212, 215, 276, 303</ref>

[[File:Vienna flak tower dsc01594.jpg|thumb|upright|left|One of eight [[flak tower]]s built during [[World War II]] in Vienna]]
[[File:The Royal Navy during the Second World War A26878.jpg|thumb|left|A British North Sea World War II [[Maunsell Fort]]]]

The Germans developed massive reinforced-concrete [[blockhouse]]s, some more than six stories high, which were known as ''[[Air raid shelter#Hochbunker|Hochbunker]]'' 'high bunkers' or "''Flaktürme''{{-"}} [[flak tower]]s, on which they placed anti-aircraft artillery. Those in cities attacked by the Allied land forces became fortresses. Several in [[Berlin]] were some of the last buildings to fall to the Soviets during the [[Battle of Berlin]] in 1945. The British built structures such as the [[Maunsell Forts]] in the [[North Sea]], the [[Thames Estuary]] and other tidal areas upon which they based guns. After the war most were left to rot. Some were outside territorial waters, and had a second life in the 1960s as platforms for [[Pirate radio in Europe#From international waters|pirate radio]] stations, while another became the base of a [[micronation]], the [[Principality of Sealand]].

[[File:B-24 Flak.jpg|thumb|right|A USAAF [[Consolidated B-24 Liberator|B-24]] bomber emerges from a cloud of flak with its No. 2 engine smoking.]]

Some nations started rocket research before World War II, including for anti-aircraft use. Further research started during the war. The first step was unguided missile systems like the British [[2-inch RP]] and 3-inch, which was fired in large numbers from ''Z batteries'', and were also fitted to warships. The firing of one of these devices during an air raid is suspected to have caused the [[Bethnal Green Tube disaster|Bethnal Green disaster]] in 1943.{{citation needed|date=April 2019}} Facing the threat of Japanese [[Kamikaze]] attacks the British and US developed surface-to-air rockets like British [[Fairey Stooge]] or the American [[SAM-N-2 Lark|Lark]] as counter measures, but none of them were ready at the end of the war. The Germans missile research was the most advanced of the war as the Germans put considerable effort in the research and development of rocket systems for all purposes. Among them were several [[List of German guided weapons of World War II|guided and unguided systems]]. Unguided systems involved the [[Fliegerfaust]] (literally "aircraft fist") rocket launcher as the first [[MANPADS]]. Guided systems were several sophisticated radio, wire, or radar guided missiles like the ''[[Wasserfall]]'' ('waterfall') rocket. Owing to the severe war situation for Germany all of those systems were only produced in small numbers and most of them were only used by training or trial units.

[[File:Ellgaard_Flak_im_Balkan_1942.jpg|thumb|right|''Flak in the Balkans, 1942'' (drawing by [[Helmuth Ellgaard]])]]

Another aspect of anti-aircraft defence was the use of [[barrage balloon]]s to act as physical obstacle initially to bomber aircraft over cities and later for ground attack aircraft over the [[Normandy Landings|Normandy invasion]] fleets. The balloon, a simple blimp tethered to the ground, worked in two ways. Firstly, it and the steel cable were a danger to any aircraft that tried to fly among them. Secondly, to avoid the balloons, bombers had to fly at a higher altitude, which was more favourable for the guns. Barrage balloons were limited in application, and had minimal success at bringing down aircraft, being largely immobile and passive defences.

The Allies' most advanced technologies were showcased by the anti-aircraft defence against the German [[V-1 flying bomb|V-1]] cruise missiles (V stands for ''Vergeltungswaffe'', 'retaliation weapon'). The 419th and 601st anti-aircraft gun battalions of the US Army were first allocated to the Folkestone-Dover coast to defend London, and then moved to Belgium to become part of the "Antwerp X" project coordinated from the {{Interlanguage link|Le Grand Veneur|nl}}<ref>{{Cite web |url=https://www.youtube.com/watch?v=DxZdUuUDMcI |title=Le Grand Veneur Keerbergen operation Antwerp X |website=YouTube |date=25 January 2014 |access-date=16 March 2016 |archive-url=https://web.archive.org/web/20161115093236/https://www.youtube.com/watch?v=DxZdUuUDMcI |archive-date=15 November 2016 |url-status=live }}</ref> in [[Keerbergen]]. With the liberation of Antwerp, the port city immediately became the highest priority target, and received the largest number of V-1 and V-2 missiles of any city. The smallest tactical unit of the operation was a gun battery consisting of four 90&nbsp;mm guns firing shells equipped with a radio [[proximity fuse]]. Incoming targets were acquired and automatically tracked by [[SCR-584 radar]],. Output from the gun-laying radar was fed to the [[M9 Gun Director]], an electronic analogue computer to calculate the lead and elevation corrections for the guns. With the help of these three technologies, close to 90% of the V-1 missiles, on track to the defence zone around the port, were destroyed.<ref>''Cruise Missile Defence: Defending Antwerp against the V-1'', Lt. Col. John A. Hamilton</ref><ref>''The Defense of Antwerp Against the V-1 Missile'', R.J. Backus, LTC, Fort Leavenworth, KS, 1971</ref>

=== Post-war ===
[[File:RIM-8 Talos launched.JPEG|right|thumb|A 1970s-era [[RIM-8 Talos|Talos]] anti-aircraft missile, fired from a [[cruiser]]]]
Post-war analysis demonstrated that even with newest anti-aircraft systems employed by both sides, the vast majority of bombers reached their targets successfully, on the order of 90%. While these figures were undesirable during the war, the advent of the [[nuclear bomb]] considerably altered the acceptability of even a single bomber reaching its target.

The developments during World War II continued for a short time into the post-war period as well. In particular the US Army set up a huge air defence network around its larger cities based on radar-guided 90&nbsp;mm and 120&nbsp;mm guns. US efforts continued into the 1950s with the 75&nbsp;mm [[M51 Skysweeper|Skysweeper]] system, an almost fully automated system including the radar, computers, power, and auto-loading gun on a single powered platform. The Skysweeper replaced all smaller guns then in use in the Army, notably the 40&nbsp;mm Bofors. By 1955, the US military deemed the 40&nbsp;mm Bofors obsolete due to its reduced capability to shoot down jet powered aircraft, and turned to SAM development, with the [[MIM-3 Nike Ajax|Nike Ajax]] and the [[RSD 58|RSD-58]]. In Europe NATO's Allied Command Europe developed an integrated air defence system, NATO Air Defence Ground Environment (NADGE), that later became the [[NATO Integrated Air Defense System|NATO Integrated Air Defence System]].

The introduction of the guided missile resulted in a significant shift in anti-aircraft strategy. Although Germany had been desperate to introduce anti-aircraft missile systems, none became operational during World War II. Following several years of post-war development, however, these systems began to mature into viable weapons. The US started an upgrade of their defences using the Nike Ajax missile, and soon the larger anti-aircraft guns disappeared. The same thing occurred in the [[Soviet Union|USSR]] after the introduction of their [[SA-2 Guideline]] systems.

[[File:Type 91 SAM fire.JPG|thumb|left|upright=0.9|A three-person [[Japan Air Self-Defense Force|JASDF]] fireteam practices using a rocket target with a training variant of a [[Type 91 surface-to-air missile|Type 91 Kai]] [[Man-portable air-defense system|MANPADS]] during an exercise at [[Eielson Air Force Base]], Alaska, as part of Red Flag – Alaska]]

As this process continued, the missile found itself being used for more and more of the roles formerly filled by guns. First to go were the large weapons, replaced by equally large missile systems of much higher performance. Smaller missiles soon followed, eventually becoming small enough to be mounted on armoured cars and tank chassis. These started replacing, or at least supplanting, similar gun-based [[SPAAG]] systems in the 1960s, and by the 1990s had replaced almost all such systems in modern armies. Man-portable missiles, MANPADS, as they are known today, were introduced in the 1960s and have supplanted or replaced even the smallest guns in most advanced armies.

In the 1982 [[Falklands War]], the Argentine armed forces deployed the newest west European weapons including the 35&nbsp;mm [[Oerlikon GDF|Oerlikon GDF-002 twin cannon]] and [[Roland (missile)|Roland missile]]. The [[Rapier (missile)|Rapier]] missile system was the primary GBAD system, used by both British artillery and RAF regiment, a few brand-new [[FIM-92 Stinger]] were used by British special forces. Both sides also used the [[Blowpipe (missile)|Blowpipe missile]]. British naval missiles used included [[Sea Dart]] and the older [[Seaslug (missile)|Sea Slug]] longer range systems, [[Seacat (missile)|SeaCat]] and the new [[Sea Wolf (missile)|Sea Wolf]] short range systems. Machine guns in AA mountings were used both ashore and afloat.

During the [[2008 South Ossetia war]] air power faced off against powerful SAM systems, like the 1980s [[Buk-M1]].

In February 2018, an Israeli F-16 fighter was downed in the occupied [[Golan Heights]] province, after it had attacked an Iranian target in Syria.<ref name='A2'>{{cite news |title=Israeli F-16 jet shot down by Syria fire, says military |url=https://www.aljazeera.com/news/2018/02/israel-shot-iranian-drone-syria-180210053946323.html |access-date=14 March 2019 |agency=Aljazeera |publisher=aljazeera.com |date=10 February 2018 |archive-url=https://web.archive.org/web/20190521214239/https://www.aljazeera.com/news/2018/02/israel-shot-iranian-drone-syria-180210053946323.html |archive-date=21 May 2019 |url-status=live }}</ref><ref name='A6'>{{cite news |last1=Lubell |first1=Maayan |last2=Barrington |first2=Lisa |title=Israeli jet shot down after bombing Iranian site in Syria |url=https://www.reuters.com/article/us-israel-iran/israeli-jet-shot-down-after-bombing-iranian-site-in-syria-idUSKBN1FU07L |access-date=14 March 2019 |work=Reuters |publisher=reuters.com |date=10 February 2018 |archive-url=https://web.archive.org/web/20190303140719/https://www.reuters.com/article/us-israel-iran/israeli-jet-shot-down-after-bombing-iranian-site-in-syria-idUSKBN1FU07L |archive-date=3 March 2019 |url-status=live }}</ref><ref name='A1'>{{cite news |title=Israeli jet crashes after attacking Iranian targets in Syria |url=https://www.france24.com/en/20180210-israel-syria-iran-air-strike-fighter-jet-f16-drone |access-date=14 March 2019 |agency=France24 |publisher=france24.com |date=10 February 2018 |archive-url=https://web.archive.org/web/20181218183450/https://www.france24.com/en/20180210-israel-syria-iran-air-strike-fighter-jet-f16-drone |archive-date=18 December 2018 |url-status=live }}</ref><ref name='A7'>{{cite news |author=Toi Staff |title=Pilot of downed F-16 jet regains consciousness, taken off respirator |url=https://www.timesofisrael.com/pilot-of-downed-f-16-jet-regains-consciousness-taken-off-respirator/ |access-date=14 March 2019 |agency=The times of Israel |publisher=timesofisrael.com |date=11 February 2018 |archive-url=https://web.archive.org/web/20180213080808/https://www.timesofisrael.com/pilot-of-downed-f-16-jet-regains-consciousness-taken-off-respirator/ |archive-date=13 February 2018 |url-status=live }}</ref> In 2006, Israel also lost a helicopter over Lebanon, shot down by a Hezbollah rocket.<ref name='A8'>{{cite news |title=Syria shoots down Israeli warplane as conflict escalates |url=https://www.bbc.com/news/world-middle-east-43014081 |access-date=15 March 2019 |agency=BBC News |publisher=bbc.com |date=10 February 2018 |archive-url=https://web.archive.org/web/20190406010625/https://www.bbc.com/news/world-middle-east-43014081 |archive-date=6 April 2019 |url-status=live }}</ref>

== AA warfare systems ==
[[File:Flugabwehrkanonenpanzer Gepard.jpg|thumb|A [[Flakpanzer Gepard|Gepard]] in motion at the 2015 Military Day in [[Uffenheim]]. The Gepard is an autonomous all-weather-capable German [[self-propelled anti-aircraft gun]] system armed with twin [[Oerlikon GDF]].]]
[[File:Bangladesh Army CS AA3 35 mm AA gun with the FW-2 fire control system on display.jpg|thumb|[[Bangladesh Army]] CS/AA3 35 mm twin anti-aircraft gun system along with its FW-2 [[fire control radar]] system behind. CS/AA3 is a Chinese variant of the Oerlikon GDF.]]

Although the firearms used by the infantry, particularly machine guns, can be used to engage low altitude air targets, on occasion with notable success, their effectiveness is generally limited and the muzzle flashes reveal infantry positions. Speed and altitude of modern jet aircraft limit target opportunities, and critical systems may be armoured in aircraft designed for the [[Ground-attack aircraft|ground attack role]]. Adaptations of the standard [[autocannon]], originally intended for air-to-ground use, and heavier [[artillery]] systems were commonly used for most anti-aircraft gunnery, starting with standard pieces on new mountings, and evolving to specially designed guns with much higher performance prior to World War II.

The [[shell (projectile)|shells]] fired by these weapons are usually fitted with different types of [[Fuse (explosives)|fuses]] ([[Barometric pressure|barometric]], time-delay, or [[proximity fuse|proximity]]) to explode close to the airborne target, releasing a shower of fast metal fragments. For shorter-range work, a lighter weapon with a higher [[rate of fire]] is required, to increase a hit probability on a fast airborne target. Weapons between [[20 mm caliber|20&nbsp;mm]] and 40&nbsp;mm calibre have been widely used in this role. Smaller weapons, typically .50 calibre or even 8&nbsp;mm rifle calibre guns have been used in the smallest mounts.

Unlike the heavier guns, these smaller weapons are in widespread use due to their low cost and ability to quickly follow the target. Classic examples of autocannons and large calibre guns are the [[Bofors 40 mm L/60 gun|40&nbsp;mm autocannon from Bofors]] and the [[8.8 cm Flak 18/36/37/41|8.8&nbsp;cm FlaK 18, 36 gun]] designed by Krupp. Artillery weapons of this sort have for the most part been superseded by the effective surface-to-air missile systems that were introduced in the 1950s, although they were still retained by many nations. The development of surface-to-air missiles began in [[Nazi Germany]] during the late World War II with missiles such as the [[Wasserfall]], though no working system was deployed before the war's end, and represented new attempts to increase effectiveness of the [[anti-aircraft|anti-aircraft systems]] faced with growing threat from [[bomber]]s. Land-based SAMs can be deployed from fixed installations or mobile launchers, either wheeled or tracked. The tracked vehicles are usually armoured vehicles specifically designed to carry SAMs.

Larger SAMs may be deployed in fixed launchers, but can be towed/re-deployed at will. The SAMs launched by individuals are known in the United States as the Man-Portable Air Defence Systems (MANPADS). MANPADS of the former Soviet Union have been exported around the World, and can be found in use by many armed forces. Targets for non-ManPAD SAMs will usually be acquired by air-search [[radar]], then tracked before/while a SAM is "locked-on" and then fired. Potential targets, if they are military aircraft, will be [[Identification Friend or Foe|identified as friend or foe]] before being engaged. The developments in the latest and relatively cheap short-range missiles have begun to replace autocannons in this role.

[[File:Anti aircraft Leningrad 1941.JPG|right|thumb|Soviet [[85 mm air defense gun M1939 (52-K)|85mm]] anti-aircraft guns deployed in the neighborhood of [[Saint Isaac's Cathedral|St Isaac's Cathedral]] during the [[Siege of Leningrad]] (formerly Petrograd, now called St. Petersburg) in 1941.]]
The interceptor aircraft (or simply interceptor) is a type of [[fighter aircraft]] designed specifically to intercept and destroy enemy aircraft, particularly [[bomber aircraft|bombers]], usually relying on high speed and [[Altitude#Altitude in aviation and in spaceflight|altitude]] capabilities. A number of jet interceptors such as the [[F-102 Delta Dagger]], the [[F-106 Delta Dart]], and the [[Mikoyan-Gurevich MiG-25|MiG-25]] were built in the period starting after the end of World War II and ending in the late 1960s, when they became less important due to the shifting of the [[strategic bombing]] role to [[ICBM]]s. Invariably the type is differentiated from other fighter aircraft designs by higher speeds and shorter operating ranges, as well as much reduced ordnance payloads.

The [[radar]] systems use [[electromagnetic radiation|electromagnetic]] waves to identify the range, altitude, direction, or speed of aircraft and [[Weather forecasting|weather formations]] to provide tactical and operational warning and direction, primarily during defensive operations. In their functional roles they provide target search, threat detection, [[Missile guidance#Radar homing|guidance]], [[reconnaissance]], [[radar navigation|navigation]], [[instrumentation]], and [[weather radar|weather reporting]] support to combat operations.

=== {{anchor|AUDS}} Anti-UAV defences ===
{{See also|Unmanned aerial vehicle#Counter unmanned air system}}

An ''anti-UAV defence system'' (AUDS) is a system for defence against military [[unmanned aerial vehicle]]s. A variety of designs have been developed, using lasers,<ref>{{cite web|last1=Sweetman|first1=Bill|title=Lasers Technology Targets Mini-UAVs|url=http://aviationweek.com/defense/lasers-technology-targets-mini-uavs|website=[[Aviation Week]]|access-date=11 March 2017|language=en|date=2 April 2015|archive-url=https://web.archive.org/web/20161214111718/http://aviationweek.com/defense/lasers-technology-targets-mini-uavs|archive-date=14 December 2016|url-status=live}}</ref> net-guns and air-to-air netting, signal jamming, and hi-jacking by means of in-flight hacking.<ref name="popmech">{{cite web|last1=Schechter|first1=Erik|title=What's Really the Best the Way to Take Down a Drone?|url=http://www.popularmechanics.com/flight/drones/a20194/best-the-way-to-take-out-a-drone/|website=[[Popular Mechanics]]|access-date=11 March 2017|language=en|date=5 April 2016|archive-url=https://web.archive.org/web/20170313223006/http://www.popularmechanics.com/flight/drones/a20194/best-the-way-to-take-out-a-drone/|archive-date=13 March 2017|url-status=live}}</ref> Anti-UAV defence systems have been deployed against [[Islamic State of Iraq and the Levant|ISIL]] drones during the [[Battle of Mosul (2016–2017)]].<ref>{{cite web|title=AUDS Counter UAV System by Blighter {{sic|spo|ted|nolink=y}} in Mosul Iraq|url=https://twitter.com/CT_operative/status/840257662172426241|website=Twitter|access-date=11 March 2017|language=en|archive-url=https://web.archive.org/web/20170315045522/https://twitter.com/CT_operative/status/840257662172426241|archive-date=15 March 2017|url-status=live}}</ref><ref>{{cite web|title=Blighter® AUDS Anti-UAV Defence System|url=http://www.blighter.com/products/auds-anti-uav-defence-system.html|website=www.blighter.com|language=en-gb|date=2016|access-date=11 March 2017|archive-url=https://web.archive.org/web/20170312062141/http://www.blighter.com/products/auds-anti-uav-defence-system.html|archive-date=12 March 2017|url-status=live}}</ref>

Alternative approaches for dealing with UAVs have included using a shotgun at close range, and for smaller drones, training eagles to snatch them from the air.<ref name="popmech"/> This only works on relatively small UAVs and [[loitering munition]]s (also called "suicide drones"). Larger UCAVs such as the [[MQ-1 Predator]] can be (and frequently are) shot down like manned aircraft of similar sizes and flight profiles.<ref>{{cite news |last=Everstine |first=Brian |date=29 June 2015|title=Air Force: Lost Predator was shot down in Syria |url=https://www.airforcetimes.com/news/pentagon-congress/2015/06/29/air-force-lost-predator-was-shot-down-in-syria/ |work=Air Force Times |access-date=18 November 2021}}</ref><ref>{{cite news |last1=Smith |first1=Saphora |last2=Kube |first2=Courtney |last3=Gubash |first3=Charlene |last4=Gains |first4=Mosheh |date=21 August 2019 |title=U.S. military drone shot down over Yemen, officials say |url=https://www.nbcnews.com/news/world/u-s-military-drone-shot-down-over-yemen-officials-say-n1044726 |work=NBC News |access-date=18 November 2021}}</ref>

[[File:Royal Navy Type 45 destroyer HMS Daring MOD 45154175.jpg|thumb|left|The [[Royal Navy]]'s [[Type 45 destroyer]]s are advanced air defence ships]]

=== Future developments ===
Guns are being increasingly pushed into specialist roles, such as the Dutch [[Goalkeeper CIWS]], which uses the [[GAU-8 Avenger]] 30&nbsp;mm seven-barrel [[Gatling gun]] for last ditch anti-missile and anti-aircraft defence. Even this formerly front-line weapon is currently being replaced by new missile systems, such as the [[RIM-116 Rolling Airframe Missile]], which is smaller, faster, and allows for mid-flight course correction (guidance) to ensure a hit. To bridge the gap between guns and missiles, Russia in particular produces the [[Kashtan CIWS]], which uses both guns and missiles for final defence with two six-barrelled 30&nbsp;mm [[Gryazev-Shipunov GSh-6-30|Gsh-6-30]] rotary canon and eight [[9M311]] surface-to-air missiles provide for its defensive capabilities.

Upsetting this development to all-missile systems is the current move to [[stealth aircraft]]. Long range missiles depend on long-range detection to provide significant lead. Stealth designs cut detection ranges so much that the aircraft is often never even seen, and when it is, it is often too late for an intercept. Systems for detection and tracking of stealthy aircraft are a major problem for anti-aircraft development.

However, as [[stealth technology]] grows, so does anti-stealth technology. Multiple transmitter radars such as those from [[bistatic radar]]s and [[low-frequency radar]]s are said to have the capabilities to detect stealth aircraft. Advanced forms of [[thermographic camera]]s such as those that incorporate [[Quantum well infrared photodetector|QWIPs]] would be able to optically see a stealth aircraft regardless of the aircraft's [[radar cross-section]] (RCS). In addition, side-looking radars, high-powered [[optical]] [[satellite]]s, and sky-scanning, high-[[aperture]], high sensitivity [[radar]]s such as [[radio telescope]]s, would all be able to narrow down the location of a stealth aircraft under certain parameters.<ref>{{cite web|url=http://homepage.mac.com/ardeshir/Anti-StealthTechnology.pdf |title=Anti-Stealth Technology |access-date=15 August 2010 |url-status=dead |archive-url=https://web.archive.org/web/20111104184517/http://homepage.mac.com/ardeshir/Anti-StealthTechnology.pdf |archive-date=4 November 2011 }}</ref> The newest SAMs have a claimed ability to be able to detect and engage stealth targets, with the most notable being the Russian [[S-400 (SAM)|S-400]], which is claimed to be able to detect a target with a 0.05-square metre RCS from 90&nbsp;km away.<ref name="aus">{{cite journal|author=Carlo Kopp |date=November 2003 |title=Asia's new SAMs |journal=Australian Aviation |page=30 |url=http://www.ausairpower.net/TE-Asia-Sams-Pt2.pdf |access-date=9 July 2006 |archive-url=https://web.archive.org/web/20060723191844/http://www.ausairpower.net/TE-Asia-Sams-Pt2.pdf |archive-date=23 July 2006 |url-status=dead }}</ref>

Another potential weapon system for anti-aircraft use is the [[laser]]. Although air planners have imagined lasers in combat since the late 1960s, only the most modern laser systems are currently reaching what could be considered "experimental usefulness". In particular the [[Tactical High Energy Laser]] can be used in the anti-aircraft and anti-missile role. The [[ALKA (weapon)|ALKA]]  [[directed-energy weapon]] (DEW) system is a Turkish dual electromagnetic/laser weapon developed by [[Roketsan]] allegedly used to destroy one of [[General National Congress|GNC's]] [[Wing Loong II]] [[Unmanned Aerial Vehicle|UAVs]]; if true, this would represent the first known time a vehicle mounted combat laser was used to destroy another combat vehicle during genuine wartime conditions.<ref>{{Cite web|last=Peck|first=Michael|date=1 September 2019|title=Did A Turkish Combat Laser Shoot Down A Chinese Drone?|url=https://nationalinterest.org/blog/buzz/did-turkish-combat-laser-shoot-down-chinese-drone-77286|access-date=2022-03-17|website=The National Interest|language=en}}</ref>

The future of projectile based weapons may be found in the [[railgun]]. Currently tests are underway on developing systems that could create as much damage as a [[Tomahawk (missile family)|Tomahawk]], but at a fraction of the cost. In February 2008 the [[US Navy]] tested a railgun; it fired a shell at {{convert|5600|mi|km}} per hour using 10 megajoules of energy. Its expected performance is over {{convert|13000|mi|km}} per hour muzzle velocity, accurate enough to hit a 5-metre target from {{convert|200|nmi|km}} away while shooting at 10 shots per minute. It is expected to be ready in 2020 to 2025.<ref>{{Cite book|title=The Modern Weaponry of the World's Armed Forces|last=Col. Y Udaya Chandar (Retd.)|publisher=Notion Press|year=2017|isbn=9781946983794}}</ref> These systems, while currently designed for static targets, would only need the ability to be retargeted to become the next generation of AA system.

== Force structures ==
{{Main|Air defence forces}}
Most Western and Commonwealth militaries integrate air defence purely with the traditional services of the military (i.e. army, navy and air force), as a [[Military branch|separate arm]] or as part of artillery. In the [[British Army]] for instance, air defence is part of the artillery arm, while in the [[Pakistan Army]], it was split off from the artillery to form a separate arm of its own in 1990. This is in contrast to some (largely communist or ex-communist) countries where not only are there provisions for air defence in the army, navy and air force but there are specific branches that deal only with the air defence of territory, for example, the Soviet [[Soviet Air Defence Forces|PVO Strany]]. The [[USSR]] also had a separate strategic rocket force in charge of [[thermonuclear weapon|nuclear]] [[intercontinental ballistic missile]]s.

=== Navy ===
[[File:AK-630 30 mm naval CIWS gun.JPEG|thumb|Soviet/Russian [[AK-630]] [[Close-in weapon system|CIWS (close-in weapon system)]]]]
[[File:BGT IDAS.jpg|thumb|right|Model of the multirole [[IDAS (missile)|IDAS missile]] of the [[German Navy]], which can be fired 
from submerged anti-aircraft weapon systems]] Smaller boats and ships typically have machine-guns or fast cannons, which can often be deadly to low-flying aircraft if linked to a [[radar]]-directed [[fire-control system]] [[Close-in weapon system|radar-controlled cannon]] for point defence. Some vessels like [[Aegis combat system|Aegis]]-equipped destroyers and cruisers are as much a threat to aircraft as any land-based air defence system. In general, naval vessels should be treated with respect by aircraft, however the reverse is equally true. [[Carrier battle group]]s are especially well defended, as not only do they typically consist of many vessels with heavy air defence armament but they are also able to launch [[fighter jet]]s for [[combat air patrol]] overhead to intercept incoming airborne threats.

Nations such as Japan use their SAM-equipped vessels to create an outer air defence perimeter and [[radar picket]] in the defence of its Home islands, and the United States also uses its Aegis-equipped ships as part of its [[Aegis Ballistic Missile Defense System]] in the defence of the Continental United States.

Some modern submarines, such as the [[Type 212 submarine]]s of the [[German Navy]], are equipped with surface-to-air missile systems, since helicopters and [[anti-submarine warfare]] aircraft are significant threats. The subsurface launched anti-air missile was first purposed by US Navy Rear Admiral Charles B. Momsen, in a 1953 article.<ref>{{cite magazine|magazine=Popular Mechanics|author=Hearst Magazines|title=Will the New Submarines Rule the Seas?|url=https://books.google.com/books?id=8NsDAAAAMBAJ&pg=PA74|date=August 1953|publisher=Hearst Magazines|pages=74–78}}</ref>

====Layered air defence====
[[File:RIM-67 intercepts Firebee drone at White Sands 1980.jpg|thumb|A [[RIM-67 Standard|RIM-67]] surface to air missile intercepts a [[Firebee]] drone at [[White Sands, New Mexico|White Sands]], 1980.]]

Layered air defence in naval tactics, especially within a carrier group, is often built around a system of concentric layers with the aircraft carrier at the centre. The outer layer will usually be provided by the carrier's aircraft, specifically its [[Airborne early warning and control|AEW&C]] aircraft combined with the [[Combat air patrol|CAP]]. If an attacker is able to penetrate this layer, then the next layers would come from the [[surface-to-air missile]]s carried by the carrier's escorts; the area-defence missiles, such as the [[RIM-67 Standard]], with a range of up to 100&nbsp;nmi, and the point-defence missiles, like the [[RIM-162 ESSM]], with a range of up to 30&nbsp;nmi. Finally, virtually every modern warship will be fitted with small-calibre guns, including a [[Close-in weapon system|CIWS]], which is usually a radar-controlled [[Gatling gun]] of between 20 mm and 30 mm calibre capable of firing several thousand rounds per minute.<ref>Naval Strike Forum. [https://web.archive.org/web/20140912101504/https://www.lexingtoninstitute.org/wp-content/uploads/aircraft-carrier-invulnerability.pdf "What it takes to successfully attack an American Aircraft carrier"]. Lexington Institute. p. 15</ref>

=== Army ===
{{Unreferenced section|date=February 2024}}
Armies typically have air defence in depth, from integral [[man-portable air-defense system]]s (MANPADS) such as the [[RBS 70]], [[FIM-92 Stinger|Stinger]] and [[9K38 Igla|Igla]] at smaller force levels up to army-level missile defence systems such as [[SA-10 Grumble|Angara]] and [[MIM-104 Patriot|Patriot]]. Often, the high-altitude long-range missile systems force aircraft to fly at low level, where anti-aircraft guns can bring them down. As well as the small and large systems, for effective air defence there must be intermediate systems. These may be deployed at regiment-level and consist of platoons of self-propelled anti-aircraft platforms, whether they are [[self-propelled anti-aircraft gun]]s (SPAAGs), integrated air-defence systems like [[2K22 Tunguska]] or all-in-one surface-to-air missile platforms like [[Roland (missile)|Roland]] or [[9K33 Osa|SA-8 Gecko]].

On a national level the United States Army was atypical in that it was primarily responsible for the missile air defences of the Continental United States with systems such as [[Project Nike]].

=== Air force ===
[[File:Aircraft Combat Archer (2565196807).jpg|thumb|A USAF [[Lockheed Martin F-22 Raptor|F-22A Raptor]] firing an [[AIM-120 AMRAAM|AIM-120]] air to air missile]]
Air defence by air forces is typically provided by [[fighter jet]]s carrying [[air-to-air missile]]s. However, most air forces choose to augment airbase defence with surface-to-air missile systems as they are such valuable targets and subject to attack by enemy aircraft. In addition, some countries choose to put all air defence responsibilities under the air force.

=== Area air defence ===
Area air defence, the air defence of a specific area or location, (as opposed to [[Point-defence|point defence]]), have historically been operated by both armies ([[Anti-Aircraft Command]] in the British Army, for instance) and Air Forces (the [[United States Air Force]]'s [[CIM-10 Bomarc]]). Area defence systems have medium to long range and can be made up of various other systems and networked into an area defence system (in which case it may be made up of several short range systems combined to effectively cover an area). An example of area defence is the defence of Saudi Arabia and Israel by [[MIM-104 Patriot]] missile batteries during the first [[Gulf War]], where the objective was to cover populated areas.

== Tactics ==

=== Mobility ===
{{Unreferenced section|date=February 2024}}[[File:Pantsir-S1 SAM at Engineering Technologies 2012.jpg|thumb|The Russian [[Pantsir-S1]] can engage targets while moving, thus achieving high survivability.]]
Most modern air defence systems are fairly mobile. Even the larger systems tend to be mounted on trailers and are designed to be fairly quickly broken down or set up. In the past, this was not always the case. Early missile systems were cumbersome and required much infrastructure; many could not be moved at all. With the diversification of air defence there has been much more emphasis on mobility. Most modern systems are usually either self-propelled (i.e. guns or missiles are mounted on a truck or tracked chassis) or towed. Even systems that consist of many components ([[Transporter erector launcher|transporter/erector/launchers]], [[radar]]s, command posts etc.) benefit from being mounted on a fleet of vehicles. In general, a fixed system can be identified, attacked and destroyed whereas a mobile system can show up in places where it is not expected. Soviet systems especially concentrate on mobility, after the lessons learnt in the [[Vietnam War]] between the US and Vietnam with the [[SA-2 Guideline]].

=== Air defence versus air defence suppression ===
[[File:AGM-88 and AIM-9 on Tornado.jpg|thumb|[[AGM-88 HARM]] under the fuselage ofn a [[German Air Force|''Luftwaffe'']] [[Panavia Tornado]]]]
Many nations have developed significant tactics for [[Suppression of Enemy Air Defences|air defence suppression]]. Dedicated weapons such as [[anti-radiation missile]]s and advanced [[electronics intelligence]] and [[electronic countermeasures]] platforms seek to suppress or negate the effectiveness of an opposing air-defence system. It is an arms race; as better jamming, countermeasures and anti-radiation weapons are developed, so are better SAM systems with [[Electronic counter-countermeasure|ECCM]] capabilities and the ability to shoot down anti-radiation missiles and other munitions aimed at them or the targets they are defending.

===Insurgent tactics===
[[FIM-92 Stinger|Stinger missiles]] supplied by the United States were used against the aircraft of the Soviet Union by the [[Afghan mujahidin|Afghan ''mujahideen'']] during the Soviet occupation of Afghanistan in the Cold War. [[Rocket-propelled grenades]] (RPGs) can be—and often are—used against hovering helicopters (e.g., by Somali militiamen during the [[Battle of Mogadishu (1993)|1993 Battle of Mogadishu]]. Firing an RPG at steep angles poses a danger to the user, because the backblast from firing reflects off the ground. In Somalia, militia members sometimes welded a steel plate onto the exhaust end of an RPG's tube to deflect pressure away from the shooter when shooting up at US helicopters.{{Citation needed|date=February 2024}} RPGs are used in this role only when more effective weapons are not available.

Another example of using RPGs against helicopters is [[Operation Anaconda]] in March 2002 in Afghanistan. Taliban insurgents defending [[Shah-i-Kot Valley]] used RPGs in a direct fire role against landing helicopters. Four rangers were killed<ref>{{Cite web|title=Stacked Up Over Anaconda|url=https://www.airforcemag.com/article/stackedupoveranaconda/|access-date=2020-10-02|website=Air Force Magazine|language=en-US}}</ref> when their helicopter was shot down by an RPG, and SEAL team member Neil C. Roberts fell out of his helicopter when it was hit by two RPGs.<ref>{{Cite web |url=https://sites.duke.edu/agsp/files/2013/11/Operation-Anaconda-Overview.pdf |title=Operation Anaconda Overview |access-date=27 January 2020 |archive-date=10 October 2015 |archive-url=https://web.archive.org/web/20151010141500/http://sites.duke.edu/agsp/files/2013/11/Operation-Anaconda-Overview.pdf |url-status=dead }}</ref> In other instances helicopters have been shot down in Afghanistan during a mission<ref>{{Cite web|date=14 October 2011|title=Investigation Confirms RPG Downed Chinook|url=https://www.airforcemag.com/investigationconfirmsrpgdownedchinook/|access-date=2020-10-02|website=Air Force Magazine|language=en-US}}</ref> in Wardak province. One feature that makes RPGs useful in air defence is that they are fused to automatically detonate at 920 m.<ref>{{Cite web|url=https://odin.tradoc.army.mil/WEG/Asset/RPG-7_Russia_Rocket-Propelled_Grenade_Launcher|title = ODIN – OE Data Integration Network}}</ref> If aimed into the air this causes the warhead to airburst which can release a limited but potentially damaging amount of shrapnel hitting a helicopter landing or taking off.{{Citation needed|date=February 2024}}

For insurgents the most effective method of [[Offensive counter air|countering aircraft]] is to attempt to destroy them on the ground, either by penetrating an airbase perimeter and destroying aircraft individually, e.g. the [[September 2012 Camp Bastion raid]], or finding a position where aircraft can be engaged with indirect fire, such as mortars.  A recent trend emerging during the [[Syrian Civil War]] is the use of [[ATGM]] against landing helicopters.<ref>{{cite tweet |last=Kaaman |first=Hugo |user=HKaaman |number=997447259150258176 |date=18 May 2018 |title=Anti-Tank Guided Missile (ATGM) strikes on helicopters during the Syrian Civil War – I made a short compilation detailing the 8 recorded ATGM strikes on helicopters in Syria. 3 strikes on parked helis, 2 on landing helis, 2 on helis after emergency landings & 1 on heli in-flight https://t.co/Za6azGABVV |language=en |access-date=31 December 2020}}</ref>

== See also ==
* [[Defence Forces#Air Defence Forces|Air defence forces]]
* [[Air supremacy]]
* [[Gun laying]]
* [[List of anti-aircraft weapons]]
* [[Self-propelled anti-aircraft weapon]]
* [[The bomber will always get through]]

== References ==
=== Citations ===
{{Reflist |colwidth = 30em }}

=== Sources ===
{{refbegin}}
* AAP-6 NATO Glossary of Terms. 2009.
* {{cite book |last=Bellamy |first=Chris |year=1986 |title=The Red God of War&nbsp;– Soviet Artillery and Rocket Forces |location=London |publisher=Brassey's}}
* Bethel, Colonel HA. 1911. "Modern Artillery in the Field". London: Macmillan and Co Ltd
* Checkland, Peter and Holwell, Sue. 1998. "Information, Systems and Information Systems&nbsp;– making sense of the field". Chichester: Wiley
*{{cite book  |first=Norman |last=Friedman |title= Naval Anti-Aircraft Guns & Gunnery |publisher = Seaforth |date=2014 |isbn= 9781473852846  }}
* Gander, T 2014. "The Bofors gun", 3rd edn. Barnsley, South Yorkshire: Pen & Sword Military.
* Hogg, Ian V. 1998. "Allied Artillery of World War Two". Malborough: The Crowood Press {{ISBN|1-86126-165-9}}
* Hogg, Ian V. 1998. "Allied Artillery of World War One" Malborough: The Crowood Press {{ISBN|1-86126-104-7}}
* {{cite book |last=Hogg |first=Ian V. |author-link=Ian V. Hogg |year=1997 |title=German Artillery of World War Two |location=London |publisher=[[Greenhill Books]] |isbn=1-85367-261-0}}
* {{cite book |last=Routledge |first=Brigadier NW. |year=1994 |title=History of the Royal regiment of Artillery&nbsp;– Anti-Aircraft Artillery 1914–55 |location=London |publisher=Brassey's |isbn=1-85753-099-3}}
* Handbook for the Ordnance, Q.F. 3.7-inch Mark II on Mounting, 3.7-inch A.A. Mark II&nbsp;– Land Service. 1940. London: War Office 26|Manuals|2494
* History of the Ministry of Munitions. 1922. Volume X The Supply of Munitions, Part VI Anti-Aircraft Supplies. Reprinted by Naval & Military Press Ltd and Imperial War Museum.
* Flavia Foradini: ''I bunker di Vienna", Abitare 2/2006, Milano
* Flavia Foradini, Edoardo Conte: ''I templi incompiuti di Hitler", catalogo della mostra omonima, Milano, Spazio Guicciardini, 17.2–13 March 2009
{{refend}}

== External links ==
{{Commons category|Air defense}}
* {{YouTube|id=ywzk73ahf00|title="Flak (1943)"}}
* [http://alsace1418.fr ''1914 1918 war in Alsace – The Battle of Linge 1915 – The 63rd Anti Aircraft Regiment in 14 18 – The 96th poste semi-fixed in the Vosges'']
* [https://web.archive.org/web/20080122025924/http://aupress.au.af.mil/catalog/books/Werrell_B28.htm ''Archie to SAM: A Short Operational History of Ground-Based Air Defense''] by Kenneth P. Werrell (book available for download)
* [http://www.j-aircraft.com/research/david_dickson/aa_doctrine.htm Japanese Anti-aircraft land/vessel doctrines in 1943–44]
* [http://www.antiaircraft.org.au/ 2nd/3rd Australian Light Anti-Aircraft Regiment]

{{Weapons}}
{{Military branches|state=expanded}}
{{Authority control}}

{{DEFAULTSORT:Anti-Aircraft Warfare}}
[[Category:Anti-aircraft warfare| ]]
[[Category:Military aviation]]
[[Category:Warfare by type]]