Naval Anti-Aircraft Guns and Gunnery. Norman Friedman

as battleships and, to a lesser extent, cruisers (slow merchant ships were another story). On this basis the Royal Navy could afford not to develop a dual-purpose destroyer main battery. As the air threat escalated, it seemed to be enough for destroyers to support heavy ships with relatively low-angle fire – the Royal Navy classified the 40° elevation guns aboard ‘Tribal’ class destroyers as fleet anti-aircraft assets, and it developed an anti-aircraft fire-control system for such ships. It is not clear to what extent the inter-war Royal Navy saw carrier-borne fighters as part of fleet air defence. Its carriers worked in close formation with its battleships, and until the late 1930s it was reasonable to imagine that screening destroyers would spot enemy aircraft in time to launch defending fighters (as the contemporary US Navy imagined). That was why the Skua was expected to assist in fleet air defence by destroying the threat at source, rather than (usually) defending the fleet directly. Once a European war seemed to be looming, neither attack at source or direct defence seemed workable. Ironically, that was exactly when radar appeared. It solved the air-warning problem, and thus made direct fighter defence entirely workable.

      While it was developing the HACS, the Royal Navy deployed an interim system employing a simple director and calculating instruments. It occupies the upper control level in this early 1927 photograph of the new battleship Nelson. The director is the thimble-shaped structure at the fore end of the platform. The earlier battleships were similarly fitted.

      Targets

      Like the other major navies, the Royal Navy did not experience air-sea warfare between 1918 and 1939. How well it prepared for the war it fought after 1939 depended in part on how realistically it could test anti-aircraft fire control and guns. Most targets were inexpensive but also unrealistic: puffs of smoke, gliders and towed sleeves (banners). The only targets which came close to realism were radio-controlled drones. The Royal Navy was the first in the world to employ them. In the early 1920s the navy began to launch radio-controlled aircraft, initially intended as anti-ship missiles, from the destroyer Stronghold.⁴ At this stage there was no real prospect of immediately turning the aircraft into realistic targets. It did not help that naval aviation was largely removed from the Royal Navy under the aegis of the RAF, because that eliminated the interaction between aviators and seamen which might have informed both. The navy did provide many of the aircrew of the Fleet Air Arm, but they did not go on to become senior naval officers. That affected the fleet’s expectations in air matters – including targets. Control by the RAF strictly limited the number of naval aircraft, precluding the use of numbers of expendable obsolete airframes as radio-controlled targets.

      Work on radio-controlled targets seems not to have resumed until about 1930. In 1932 the RAF modified three standard fleet floatplanes (Fairey IIIFs called Fairey Queens) into radio-controlled drones. The first two were damaged beyond repair while being catapulted by the battleship Valiant, but the third was successfully launched in the autumn. It made a short trial flight, which demonstrated that it could be controlled in the air and landed on its float. Arrangements were made to use it as a Home Fleet target off Gibraltar during the 1933 Spring Cruise, and plans were made to develop a smaller and less expensive drone which could be maintained by RAF and Fleet Air Arm personnel.

      The cruiser Sussex shot down the sole Fairey Queen late in May 1933 on the ninth salvo of Run 2. The ship had 48 per cent of her bursts within 100 yds during Run 1 and 59 per cent during Run 2 (100 yds was considered satisfactory). As a result of the Fairey Queen trials, the Air Ministry carried out further trials with radio-controlled De Havilland Moths which were called Queen Bees. Four were to be made available to the Mediterranean Fleet in June 1934, and four more to the Home Fleet in the autumn of that year. Unfortunately these targets could not simulate dive bombing.

      Initial experiments showed that anti-aircraft effectiveness was much less than had been imagined. Reporting on Queen Bee firings in the Mediterranean, Vice Admiral 1st Battle Squadron pointed out that the standard of placing rounds within 100 yds of a target was misleading. In one exercise, although 59 per cent were within 100 yds, only 1.56 per cent would have scored actual hits. No more than a quarter of 4in shells within 100 yds would cause damage to an aircraft, and the other three-quarters should be scored as close misses. The fleet commander agreed; probably only th of these shells would damage an aircraft. Experiments by the all-service Ordnance Committee showed that a 4in HE shell had to burst within 70ft to cause decisive damage, and outside 140ft there would probably be no damage at all. The 100 yd standard had been adopted because it was impossible to determine the position of a shell burst any more accurately – the percentage within 100 yds was really no more than a way of assessing accuracy.

      The more subtle message, illuminated by somewhat later US experience, was that with so few targets available, there was little interest in shooting them down. The fleet did not learn the lesson the US Navy learned from its own drones, that advertised shell lethality had been badly overstated. The typical test method, bursting a shell near an aircraft near the ground, was not at all good enough.

      The navy pressed the Air Ministry to make targets more realistic, both by enabling them to dive and to operate them in pairs. In 1935 it hoped to modify the Queen Bee to dive at angles of 35–40° at 175mph, but it could not operate two of them in formation, to simulate a mass attack.

      The navy certainly understood how different drone firings were from other forms of anti-aircraft practice, and it embraced the new technique. During 1935 a Queen Bee base was established at Vigie Creek, St. Lucia, and approval was given to recommission the old carrier Argus as a Queen Bee tender, to carry the Home Fleet Gunnery Co-Operation Unit as well as drones (she would also be the deck landing ship). No similar ship was provided to the Mediterranean Fleet because Malta offered sufficient facilities ashore. However, as aircraft speeds increased through the late 1930s, it was increasingly clear that the Queen Bee was not a particularly realistic target.

      Even without drones, it was difficult to arrange realistic practices representing aircraft flying directly towards the firing ship, as would be the case in wartime. Progress in Naval Gunnery 1932 mentioned as an important development increased numbers of exercises in which bombers flew overhead rather than as crossing targets. The Home Fleet wanted 60 per cent of cruiser shoots and 75 per cent of battleship shoots to represent aircraft directly attacking the firing ship, and there was general agreement. Apparently the problem was safety requirements which limited firing close to a ship.

      Fire Control

      Probably the most important decision of the Naval Anti-Aircraft Gunnery Committee was to abandon the barrage fire adopted during the First World War in favour of aiming directly at the aircraft. Not only did theoretical calculation show that barrage was practically useless, but results in the war were ‘too slight to be counted on’. That required something which measured aircraft motion and predicted aircraft position. The Royal Navy developed a High Angle Control System (HACS) incorporating one or more aloft directors linked with one or more High Angle Control Positions (HACPs) containing the system’s computer, the High Angle Calculating Table (HACT). The HACP was analogous to the below-decks Transmitting Station (TS) used to control main battery guns; the HACT was analogous to the new Admiralty Fire Control Table (AFCT) and its derivatives. A policy for installing HACS in new and existing ships was promulgated in 1929.⁵

      In June 1919 the Naval Anti-Aircraft Gunnery Committee formed a sub-committee to test new anti-aircraft fire-control devices.⁶ For trials, the director could be separated from the control (computing) system. The director and the associated rangefinder were the eyes of the system. They provided its inputs, and they would also be the basis of any feedback. It was not sure whether a director should incorporate a rangefinder, but decided that for trials purposes director and rangefinder could be separate. The committee wanted a means of detecting whether a target was flying level – by no means did it assume that it was. However, if the target did fly straight and level the fire-control problem was considerably simplified. Moreover, in 1919 the major air threats were level and torpedo bombing, so it made sense