The medium-calibre long-range anti-aircraft fire-control systems used in the Second World War can all be traced back to those of the inter-war years. Because very little money was available in the 1930s, the key issue was whether earlier, unsatisfactory, systems could be the basis for step-by-step development into something effective. At first glance the US Navy’s Mk 19 director (centre) flanked by two separate ‘altiscopes’ on board the heavy cruiser Chicago looks distinctly unpromising. Operators at the director looked at the target and corrected aim, but because the altiscopes (range- and heightfinders) were physically separate the director operators could never be sure that they and the altiscope operators were even tracking the same target. The connection to fuse-setters at the guns was even more tenuous. However, the tachymetric concept embodied in the director was viable. The next step was to adopt stereo rangefinders which could be installed in an integrated director, effectively combining the altiscope and an evolved Mk 19 as Mk 28 and Mk 33, the main prewar medium-calibre systems. The step beyond, which created the successful wartime Mk 37, was to clear the director by moving the computer below decks, connecting it with the director by synchros and power drives. At the same time the fire-control system was more tightly integrated with the fuse-setter, which ultimately was placed in the ammunition hoist. This photograph was taken at Mare Island in 1931. The hooded object below the anti-aircraft fire control platform was a main-battery director.
The inside of a Director Mount Mk I shows just how simple it was; the object in the foreground is largely unmodified Mk 19 director. This illustration is from the manual, issued in July 1940.
In both the United States and the United Kingdom, the impact of the Depression was to reduce training and to defer desired anti-aircraft upgrades (such as additional guns) and, more subtly but probably more importantly, to defer purchases of expendables, such as ammunition and, crucially for anti-aircraft warfare, fuses. Training time mattered enormously, not only because it determined how well systems would perform in wartime, but also because training exercises were generally the source of the navies’ expectations as to wartime system performance. They shaped what the navies thought they needed. Only at the end of the Second World War did the US Navy form a special dedicated experimental test and evaluation unit. Until then experiments and training were tied together.
For the Royal Navy, the Depression deferred the introduction of radio-controlled drone targets, which would have done a lot to make target shoots more realistic and thus might have goaded the Royal Navy towards developing more effective forms of fire control in time for the Second World War (it is not clear that the US Navy had the potential to adopt target drones much earlier than it did). The Royal Navy used its drones differently from the US Navy, and they could not simulate dive bombing. At the end of the war, the commander of the British Pacific Fleet argued that his fleet’s poor anti-aircraft performance, compared to that of the US Navy, could be traced in part to its lack of realistic anti-aircraft training (the US Navy was plentifully supplied with drones). For both navies, despite clear understanding of the consequences, it was impossible to replace powder time fuses with mechanical ones, given the huge numbers involved. The US Navy had to accept a very high rate of duds and low-order detonations, which may not have been obvious until it began using drones for target practice in 1939. As late as 1941 the Bureau of Ordnance had to warn the fleet that the next year it would have to use powder fuses for half its practice firings.1
The third major naval power, Japan, had yet a different experience. Despite the effect of the Depression, and also despite relative poverty, successive Japanese governments continued to spend heavily on their fleet. They did not spend much on developing entirely new systems, although there were major exceptions such as the ‘Long Lance’ torpedo. In particular Japan could not develop new industries such as electronics to anything like the level of the much wealthier Western powers. In effect Japan mobilised continuously between the World Wars, and it too obeyed the iron law. With important exceptions (mainly naval aviation), the Imperial Japanese Navy of 1941 was a superbly developed First World War navy. Like Britain and the United States, Japan developed radio-controlled target drones.
By 1940, with the world in crisis, the US Navy could deploy the medium-calibre system it would use during the Second World War, albeit as yet without radar. Hillary P Jones is shown on 14 December 1940. British observers were impressed by the all-dual purpose main battery and the Mk 37 fire-control system (as yet they were probably unaware of the integrated fuse-setters in the ammunition hoists). The US system included a stable vertical (a vertical reference used to stabilise the director) and RPC for the 5in guns. The British argued, however, that US destroyers were top-heavy compared to their own ships; the US Navy did not contemplate the sort of rough waters the British expected. Nos 3 and 4 mounts were unshielded in order to save weight. Notably lacking was much of an automatic battery to beat off dive bombers. This ship could accommodate a pair of 0.50-calibre machine guns on the platform below the searchlight aft. In 1940 the US Navy doubted that defence against such attack was really practicable; it expected to rely on barrage fire by medium-calibre guns. By December 1940 the Royal Navy was using such ‘umbrella barrages’ in action.
By 1941 the US Navy wanted splinter protection for all its guns. Gleaves, a sister-ship of Hillary P Jones, is shown after a Boston Navy Yard refit, 18 June 1941. Nos 3 and 4 guns are now half-shielded (they have no roofs); full gunhouses would have added too much weight. Note also the gun tubs, for 0.50-calibre machine guns, around her after stack. She had another pair of gun tubs just forward of her bridge structure on her 01 level. Her after bank of torpedo tubes had been removed as weight compensation. The next step was to replace No 3 5in gun with a pair of twin Bofors, from 1942 onwards.
More generally, aircraft were the exception to the slow development of fleets between the wars. In the 1920s and 1930s they were inexpensive, and the potential for development was huge. Particularly in the United States and in Japan, relatively small investments in naval aircraft development had huge payoffs. From the point of view of naval air defence, that meant huge changes in requirements and the obsolescence of earlier systems. Thus the Royal Navy, which had been quite air-minded and had deployed an advanced high-angle fire-control system in the 1920s, found it difficult to devise an entirely new system capable of keeping up with a rapidly-evolving threat in the 1930s. On the other hand, because the United Kingdom developed a large electronics industry between the wars, it was able to deploy radar in quantity and with high quality. Radar in turn made it possible for the Royal Navy to make up for deficiencies in anti-aircraft gunnery by controlling fighters against enemy bombers. The Imperial Japanese Navy had no such potential, because it had spent most of its money on pre-electronic forms of naval warfare.
The limited cost and rapid development potential of aircraft explain why Germany, which created a large military machine so rapidly, emphasised them both ashore and over the sea. For the Germans aircraft were also attractive because most people saw them as the embodiment of the future. Hitler and his Nazis represented themselves as the future of Germany, and it was natural for them to make the Luftwaffe integral with the Party. To some extent Mussolini had a similar view of aircraft and his air force, although the result was less successful than Hitler’s. German and Italian shore-based aircraft were the key elements of the war the Royal Navy fought in the Mediterranean.
During the Second World War it was not well understood that although aircraft might be plentiful, experienced aircrew were not. Only after the war did it become clear how devastating losses could be, particularly if new aircrew were not being trained rapidly enough. Thus after the successful ‘Turkey Shoot’ which wiped out the Japanese carrier air arm during the battle of the Philippine Sea (June 1944), US naval aircrew were depressed because they had not dealt with most of the Japanese carriers – a view which carried over into the success of the