Editing Anti-aircraft warfare (section)

=== 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]]