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 curves for different ranges. Where these curves crossed the altitude curves indicated the elevation to which a gun had to be laid to reach a given range at a set altitude.
The French called the fuse curves an abaque (abacus). They could be turned into what the British fuse curve dial: a dial graduated for time of flight on its periphery. Curves for constant burst range were inscribed on the disk. The distance from the centre of the dial indicated altitude, the curves being functions of altitude and fuse duration (time). The indicator working with the dial was graduated in altitude. The dial was turned so that the pointer was on the curve for the desired burst range. Where it touched that fuse curve indicated the duration for which a fuse should be set.
In surface fire, the gun elevated to an angle set simply by target range, but in anti-aircraft fire the problem was complicated by the fact that the aircraft was already flying above the horizon. The French concluded that nothing short of the mesh of curves would make successful fire possible. They had to add superelevation to the future angle of sight of the target. Typically a pointer was raised or lowered as the gun was pointed up at the expected future angle of sight. The gun was then elevated so that the curve corresponding to expected range on the fuse dial met the pointer.
As elsewhere, wartime French attempts at anti-aircraft fire control were based on the assumption that the target would fly straight and level. The French adopted much the same technique as the British, concentrating on plan motion. They developed alternative electric and mechanical means of measuring the rate at which the angle of sight changed, which they called tachymetres.18 Both wind and aircraft speed were measured by time a cloud and the aircraft spent passing through a measured grill at an angle set for altitude. There was also a special sight to determine target course. These techniques, reflected in army M1917 equipment, were not of course well suited to a moving, rolling ship. However, their success encouraged post-war naval projects.
The French navy ended the First World War with these devices, mainly calibrated for the army’s 75mm gun. It knew that they were ill-suited to moving ships. Neither guns nor instruments were stabilised. The navy did plan to use 2m or 4m rangefinders and direct means of measuring angle of sight.
The standard wartime French anti-aircraft gun was an adapted 47mm M1902. Its trunnions were moved to its rear, so that the gun could elevate to nearly 90°. A reflector sight was developed by the naval gunnery directorate at Toulon. The pointer kept the reflected target image in coincidence with a cross in a collimator. The reflector sight permitted a gunner to look down rather than strain to look directly up at the target. This technique was effective as long as the target remained visible in the mirror, but target acquisition could be difficult, particularly in rough weather. The collimator was arranged so that the shell would be fired ahead of the target. Firing tables were devised for a target speed of 120km/hr (74.5mph), and fire was not opened until the target was within 2000m. At about the same time Le Prieur, who was responsible for important surface fire control devices, devised a very simple machine gun sight using what would later be called a cartwheel foresight, comprising concentric circles with radii every 20 to 25°. The pointer chose the radius which most closely approached the target, and the circle representing deflections for a set speed at a given range. This device survived in widespread post-war service, in France and abroad.19
The Japanese-built Arabe class destroyers transferred to France during the war had Japanese-built versions of the British Vickers 3in gun. As noted, submarines particularly needed anti-aircraft guns. French steam submarines were particularly slow divers. The wartime Dupuy de Lôme, Gorgonne and Nereide classes were all equipped with 75mm guns derived from the army’s weapons. They were on disappearing mounts which could elevate to 80° and depress to -10°.
Germany
Unlike the Royal Navy (and all other major navies), the Germans used stereo rather than coincidence rangefinders. It is not clear to what extent the Germans applied stereo ranging to anti-aircraft defence during the First World War. They do not seem to have developed any specialised anti-aircraft fire-control system. The principal wartime anti-aircraft gun was the 8.8cm/45, originally adopted to beat off surface torpedo attacks, and then placed in a new high-angle mounting. Battleships typically had two at the beginning of the war and four at the end.
Italy
The wartime Royal Italian Navy used 76mm/40 and 76mm/45 antiaircraft guns, the former of Schneider 1911, the latter of Ansaldo 1917 type. Many submarines had 3in/30 anti-aircraft guns. The Italians licence-produced the Vickers pom-pom as the 40mm/39.
Like the larger navies, the German navy continued to use its First World War medium anti-aircraft gun during the inter-war period, in its case the 8.8cm/45. Two shielded guns of this type are shown on board the cruiser Königsberg in about 1931. By this time work was beginning on an entirely new long-barrel 8.8cm gun, which in turn was soon superseded by a long-barrel 10.5cm weapon. Unlike the later guns, which were counterbalanced so that their trunnions could be very close to their breeches, the 8.8cm/45 was of conventional design.
The 8.8cm/45 gun on board the first German post-war cruisers was a shielded version of the World War I anti-aircraft mounting. (Drawing by Mirosław Skwiot, from his German Naval Guns: 1939-1945)
The armoured cruiser San Giorgio shows two of her 3in/40 anti-aircraft guns atop her after turret. They were 12pdr 12 cwt guns of British type; the Italians also used the 3in/45, presumably the Vickers 3in 20 cwt license-built by Schneider (it was designated a Schneider gun). (Lieutenant Commander Erminio Bagnasco)
The standard Japanese naval anti-aircraft gun introduced during the First World War was the 8cm (actually 7.62cm, or 3in). This one is at the Beijing military museum. Next to it is the twin version of the standard Japanese 25mm machine gun of the Second World War. (Dr Raymond Cheung)
Japan
