Wikipedia: excerpt from Anti-aircraft Warfare On 30 September 1915, troops of the Serbian Army observed three enemy aircraft approaching Kragujevac. Soldiers shot 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 fire. 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" (a 37 mm version of the Maxim Gun). A Maxim anti-aircraft machine gun. All armies soon deployed AA guns often based on their smaller field pieces, notably the French 75 mm and Russian 76.2 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 13-pdr QF 6 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 13-pr QF 9 cwt and these proved much more satisfactory. 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.