Details mattered enormously. Most anti-aircraft guns, down to about 40mm or 37mm, were power-worked. If a ship lost power, they were nearly useless, even if they had alternative manual controls (which could not move them nearly fast enough to track targets). After HMS Prince of Wales lost power due to a very unlucky torpedo hit, her powerful light anti-aircraft battery was suddenly reduced to a single Bofors on her quarterdeck and a few Oerlikons. No wonder her gunnery officer thought that Bofors was worth all her pom-poms; but he did not realise that the only way to wield massive anti-aircraft firepower was to accept power operation. The flaw in the ship’s anti-aircraft armament turned out to be the absence of emergency diesel generators, of the type the US Navy and not the Royal Navy provided.
Similarly, the way in which fire controls and associated equipment was connected to guns mattered. Until the 1930s the Royal Navy relied entirely on step-by-step motors to transmit data, for example from a fire-control computer to a gun mount. These devices are simple and robust, but their action is abrupt, as they click from one setting to the next. The Royal Navy seems to have rejected stabilisation in anti-aircraft systems because that required smooth transmission from a stable element to the guns and directors. By the time the Royal Navy had a smooth enough form of transmission (Magslip), it was too late to reverse the earlier decision, because Britain was mobilising.
Pre-war financial restrictions precluded development of a fire-control system for the 3in/50 gun, which armed the ten Omaha class cruisers and the oldest battleships, among others. At best, these ships could only fire barrages through which, it might be hoped, an attacking aircraft might fly. As war came closer, old destroyers like Overton, shown, were rearmed with six 3in/50s – but they too had no special fire-control systems, and to describe them as anti-aircraft escorts was unfortunate at best. As late as 1943 destroyer escorts armed with 3in guns lacked any fire controls.
Much the same might be said of the British decision not to adopt stereo rangefinders for anti-aircraft fire. Coincidence rangefinders, particularly the horizontal ones used by the Royal Navy, proved ill-adapted to anti-aircraft operation. Rangefinding problems helped convince the British to accept what turned out to be a poor high-angle control system, in which target speed had to be estimated on the basis of perceived target type. Only in 1943, with the evidence of US stereo rangefinding before it, did the Admiralty admit that it should have adopted stereo techniques for air defence.
Technical details have been presented to give a clear idea of what the major navies were doing during the supposedly empty inter-war period to protect themselves against air attack. Although their efforts were not entirely effective, it is clear that they were extensive. Details also make it possible to compare different approaches, particularly those of the Royal Navy and the US Navy, in as objective a way as possible. To the greatest possible extent, this material has been taken from contemporary internal documents rather than from later ones.
For continuity, the story of systems conceived before the war has generally been continued into the Second World War in the inter-war chapters, the wartime chapters concentrating on entirely new wartime developments. Thus in the US case the various Bureau of Ordnance machine gun directors (Mks 44, 45, 49) conceived in 1940 are in the pre-war chapter, but the wartime Mk 51 and its ilk are in the wartime chapter. Similar logic applies to the other navies. Except for the US Navy and the Royal Navy, virtually all wartime equipment was of prewar conception and design.
Sources
This account concentrates on the US Navy and the Royal Navy because they were by far the most advanced exponents of anti-aircraft gunnery between the wars and during the Second World War, and because their post-war work on guns and fire control reflected their extensive wartime experience. Their story can be told almost entirely on the basis of primary documents. The quality and quantity of documentation differs considerably. Much of the US naval ordnance material, including correspondence files and weapon and fire-control handbooks, has survived, though much less has survived of publications explaining how weapons were to be used. Far less of the corresponding Royal Navy material seems to exist, but the annual official publication Progress in Naval Gunnery tells much of the story. Many British handbooks, some with no surviving US equivalents, have also survived. The rough US equivalents to Progress in Naval Gunnery are the more or less annual Bureau of Ordnance Confidential Bulletin and the voluminous annual Reports on Gunnery Exercises. For ships the most important surviving British documents are the Ships’ Covers and constructors’ notebooks. The reader should be aware that constructors showed little interest in weapon development, though Covers do occasionally include relevant material, and they also often reflect shifts in anti-aircraft thinking.
Other major navies seem much less completely documented. French archival documentation has been supplemented by some publications. The French made extensive pre-war efforts to develop anti-aircraft firepower even though they did not have much opportunity to use their systems during the Second World War. To some extent pre-war work was the basis for post-war development. Documents collected or produced by the victorious Western powers after the Second World War provide insight into developments in Germany, Italy and Japan, but information is limited. The account of Soviet developments is based on published Russian-language material, which has, fortunately, become available in quantity with the end of the Cold War.
By the end of the Second World War, the fusion of surface anti-aircraft fire and fighter defence was symbolised by radar picket destroyers like Chevalier, shown off Hampton Roads, newly converted, on 24 May 1945. A tripod radar mast replaced her forward bank of torpedo tubes; the after bank was replaced by additional anti-aircraft guns. The mast carried, top to bottom, a YE aircraft homing beacon, an SP pencil-beam aircraft-tracking and heightfinding radar, an array of enemy radar receiving antennas (on the yardarm), and a TDY jammer (on the lower platform). The fleet had discovered the value of radar picket destroyers stationed well forward of a force in the direction of a likely threat, and at Okinawa it set up fifteen radar picket (RP) stations, each of which was manned by a destroyer and supporting craft, particularly fire support landing craft (LCS). Ships in the anti-submarine and anti-surface screens were also used as radar pickets as the situation demanded. Each picket was to open fire on any unidentified aircraft which came within 12,000 yds. The destroyers were not specially fitted, but they did have fighter controllers on board. They were primarily radar guards to provide the fleet with early warning. Although not primarily fighter directors, they could be assigned to that role. Pickets were placed 75 miles from the centre of the defended area. That made it possible for them to pass control of friendly fighters from one to another, but not close enough for mutual support when attacked. The SP radar on board a specially-converted radar picket fed a more sophisticated combat information centre on board the destroyer. Destroyer radar picket losses off Okinawa were so severe that alternatives were sought for the planned invasion of Japan: either smaller and hence less valuable pickets (converted destroyer escorts) or submarines, which could submerge in the face of the worst threats. Both were in process when the war ended.