In addition to the specialised anti-aircraft guns, the 1917 Admiralty pamphlet on high-angle firing, but not its 1916 predecessor, envisaged using low-angle guns against distant aircraft; this was later an important theme in British naval anti-aircraft thinking. At low angles it was preferable to work in range rather than in altitude, and range determined the fuse length. Unfortunately the target would be moving rapidly through successive fuse-range curves, so no one fuse setting would suffice for long. Barrage fire would be the only effective tactic. To this end, larger-calibre low-angle guns were being supplied with shrapnel shell using a No. 81 fuse like that supplied for high-angle guns. The use of surface weapons controlled for barrage fire became an important theme of later British anti-aircraft development.
A 2pdr (40mm) pom-pom is shown on board a drifter during the First World War, with a heavier QF gun (a 6pdr Hotchkiss) in the background. The water-cooled pom-pom, known as such because of the noise it made as it fired, was a revived Boer War gun on a HA mounting. It was a scaled-up equivalent of the 0.303in Maxim or Vickers-Maxim used in large numbers by the British Army. This weapon armed corvettes during the Second World War, and it was also mounted in the bows of ‘Hunt’ class destroyers to deal with E-boats (German MTBs). Pom-poms were also made in other sizes, such as 1¼pdrs and 1pdrs (37mm). The 40mm Bofors was apparently conceived to meet a Royal Swedish Navy requirement for a pom-pom replacement.
The 2pdr pom-pom is shown on its standard HA single mounting. During the First World War the 2pdr was made under license in Italy (as the 40mm/39), and between the wars it was sold in quantity to Japan. Many other navies adopted it; the main exception was probably the US Navy. Until it began to offer the quadruple 0.5in gun in the late 1930s, Vickers sold the 2pdr to all navies for which it built destroyers. Some of them retained it after the war. The 2pdr appears in many armament lists as a 40mm gun.
A 2pdr pom-pom on board HMCS Assiniboine during the Second World War. During the inter-war period the 2pdr replaced the 3in gun on board British destroyers, itself being superseded by the quadruple 0.5in gun. (RCN)
The Austro-Hungarian battleship Prinz Eugen shows a black-shrouded 7cm G. L/50 anti-aircraft gun atop her ‘B’ turret. She had two more atop ‘X’ turret. By the end of the war Prinz Eugen had two guns atop ‘B’ turret and one atop ‘A’ turret. Her sister-ship Szent Istvan had the gun atop ‘A’ turret, and the other two ships each had two guns atop ‘B’ turret. Actual calibre was 6.6cm. This Skoda gun was introduced in 1911 as an anti-torpedo (boat) weapon, and was modified in 1915 as an anti-aircraft gun on a new mounting. In 1918 the standard battery of a Tegetthoff class battleship like this one was sixteen 7cm/50, including three or four on anti-aircraft mounts. Other battleships also had these weapons.
Austria-Hungary
According to a post-war report prepared for the US Navy, the Austrians concluded during the war that anti-aircraft fire could deal only with an aircraft actually attacking a ship; for anything else fighters were needed.15 It was unlikely that fire would bring the aircraft down, so the object was to deter him from dropping bombs.16 The Austrians therefore adopted barrage fire, mounting groups of four guns on board large ships. Fire was controlled by an officer at one end of the battery, with a clear view of the sky. He had tripod-mounted Zeiss binoculars for target acquisition, marked so that he could indicate target bearing and elevation, plus a Zeiss stereo rangefinder to measure range and altitude (by elevation).17 He also had printed firing tables. Ready-use shells at the guns had mechanical fuses pre-set for various times. The commander estimated target speed, and he used a pocket watch to indicate direction, the XII being pointed towards the approaching aircraft, and VI towards the observer. The control officer had printed firing tables including graphs of trajectories with various elevations and fuse settings. The tables showed required gun elevation for a given target altitude, range, speed and course. Guns fired in barrage mode, each of the four guns being assigned a different elevation. Three salvoes were fired as quickly as possible, after which the battery was re-aimed based both on spotting and on any observed aircraft manoeuvres. The control officer communicated with the battery either by megaphone or by visual signals, but the order to fire or cease fire was given either electrically or by a whistle. On ships with only one or two anti-aircraft guns, the object was only to keep the aviator from dropping bombs with any accuracy. Torpedo boat divisions formed a single battery under the command of the chief boat. In moving ships, the stress was on firing as rapidly as possible, to force the pilot to fly higher. Ships in harbour consolidated their anti-aircraft batteries with those ashore, each being assigned a sector. By the end of the war this procedure was considered somewhat unsatisfactory.
It is not clear to what, if any, extent the Austrian system matched the German. The Austrians used Barr & Stroud coincidence rangefinders for surface fire, so it seems at least possible that the Germans convinced them to adopt stereo rangefinders for anti-aircraft fire.
The Austrians deployed a wide variety of anti-aircraft guns: 7cm (of 20, 26, 30, 45 and 50 calibre lengths), 7.5cm/30, and 9cm (lengths 35 and 45 calibres). At the end of the war they were about to deploy 10cm and 12cm anti-aircraft guns. Presumably the extent of anti-aircraft armament reflects the considerable threat posed by the Italian air force. The heaviest gun in service was the 9cm (3.5in)/45, which fired a 10.2kg shell with a muzzle velocity of 600m/sec (1968ft/sec). Surface range was about 7km (7650 yds). The gun carried a device to adjust elevation angle
France
Most wartime French anti-aircraft research was sponsored by the army, which was far more affected by air attack. The French defence organisation separated armaments (the role of the current Direction Générale de l’Armament) from the services, so the responsible Mission ballistique des tirs aeriens (MBTA) had representatives from army, navy, and armaments organisation headquartered at Gâvres. The French army introduced powder time fuses and the notion of fuse curves which showed fuse duration as a function not only of target range but also of target height (gun elevation). Pre-war methods of constructing firing tables, which had been proposed as early as 1888, were poorly adapted to high-angle fire against aircraft. Given the new technique, it was possible to construct meshes of curves showing trajectories at different elevation angles. Cross-curves at different ranges showed the altitudes shells would reach at different elevation angles. Duration markers were placed along each trajectory. For a gun firing at an elevation of 40°, for example, maximum range would be something beyond 10,000m. The shell would cross the 6000m range curve after flying for slightly less than 25 seconds, and at an altitude of slightly less than 3000m. The times in a printed version of a set of curves were 25, 30 and 35 seconds, and maximum elevation given was 80°. Thus to burst a shell at a range of 6000m and an altitude slightly less than 3000m, its fuse would have to be cut for slightly under 25 seconds. The gun would be elevated to 40°. The mesh of curves showed that a demand to burst a shell at a particular range and altitude corresponded to a particular elevation and fuse setting. The French saw such meshes as the basis for a future anti-aircraft fire-control system, and they published the relevant theory in 1919–21.
The standard French Navy anti-aircraft gun of the First World War was the 47mm (3pdr) quick-firing gun on a new anti-aircraft mounting. The gun had originally been adopted as an anti-torpedo (boat) weapon, and it was comparable to the contemporary Royal Navy 3pdr. This one is shown on board the battleship Courbet in 1918.
The same data could be used to construct an alternative set of curves in which the cross-curves were arcs of a circle drawn to indicate various ranges. The arcs were calibrated in elevation angle. On this polar graph were drawn