Naval Anti-Aircraft Guns and Gunnery. Norman Friedman
the gun was at maximum elevation, and therefore by how far back the breech was from the trunnions). Since the gun would not be balanced, it would need considerable counterweight, which in turn would make for a heavier gun and mounting. Even then the gun and mounting could not be properly balanced at all elevations.
The 4.7in QF Mk VIII (4.7in/40) was the first inter-war Royal Navy medium-calibre anti-aircraft gun. Its design reflected First World War experience. It fired the largest-calibre fixed-ammunition used by the Royal Navy, although the later 4.5in QF Mk I and III fired heavier rounds. This gun armed the battleships Nelson and Rodney (hence would have armed the more numerous capital ships stopped by the Washington Treaty), the Courageous class carriers, the seaplane carrier Albatross and the minelayer Adventure. Two guns are shown on board the Australian seaplane carrier Albatross. (Alan C Green via State Library of Victoria)
Until the Spanish shipbuilding industry was nationalised in about 1935, Vickers had a majority stake in it, designing ships and weapons. It provided Spain with its own variant of the 4.7in/45, which it designated Mk F. These guns armed the two Canarias class heavy cruisers and also the rearmed cruiser Mendez Nuñez; in LA form they also armed other ships. Mk F is shown on board Mendez Nuñez (as presented in an attaché report dated 6 December 1951).
The Committee reported to DNO in June 1919 that it preferred QF (metal cartridge case rather than bagged charge) guns for rapidity of loading, simplicity of ramming and automatic breech closing. It also preferred semi-automatic operation with fixed ammunition. If the mounting was properly balanced it could be hand- rather than power-trained. A maximum elevation rate of 4°/sec was required. In October the committee pointed out that from a different point of view it was desirable to adopt the largest possible gun. Any fire-control solution reflected the motion of the aircraft up to the point of firing. The pilot might well manoeuvre as the shell rose towards him. The longer the shell took to arrive, the better the chance that it would miss altogether. To minimise time of flight, the shell should have the greatest possible muzzle velocity and also should lose its velocity as slowly as possible. The heavier the shell, the better it retained muzzle velocity. For example, at a range of 4000 yds it took a 3pdr HA shell (3½lbs) 14.5 sec to reach an aircraft at 10,000ft (muzzle velocity 2500ft/sec); a 3in shell (16lbs, 6 CRH shape) with the same muzzle velocity took 9.7 sec. Even though it had a lower muzzle velocity, a 4in HA shell (2350ft/sec, 31lbs, 6 CRH) took 7.2 seconds. The heavier shell was also less affected by wind.
All of this was aside from the fact that the danger sphere (lethal radius) of a shell was proportional to its weight (assuming it carried the largest possible burster). On this basis, in October 1919 the Committee recommended the 5.5in gun: it saw no need to limit gun size by demanding that the gun operate manually. That in turn implied that any future dual-purpose capital ship gun would be mounted in gunhouses, which could incorporate power loading and power elevation and training. Power operation in turn made it natural to link the gun automatically to the emerging computer fire-control system. In March 1920 the Committee compared existing heavy anti-aircraft guns: the standard 3in and 4in, the developmental 4.7in (2400ft/sec muzzle velocity), and the proposed 5.5in (2400ft/sec). Time of flight and remaining velocity were tabulated for guns elevated to 50°, firing at aircraft at various altitudes. Maximum altitude for the 3in gun was 15,000ft, to which time of flight would be 20.9 seconds, with a remaining velocity of 550ft/sec. That compared to 11.85 seconds for the 5.5in (1205ft/sec). All guns but the 3in could reach an aircraft at 20,000ft.
Vickers’ drawing of a 4.7in mounting is taken from its 1923 catalogue. (John A Roberts)
Repulse was fitted with the first of DNO’s BD production mountings during her 1933–6 modernisation. The top of the mounting is visible at the foot of her mainmast, protruding from the awning, its director on a pole just forward of the forward of the two triple 4in LA mountings. The ship retained four single 4in guns, and was fitted with the pair of octuple pom-poms standard in capital ships at the time. Note the single 4in HA Mk V gun visible abeam the fore funnel, and also the apertures for the above-water torpedo tubes. The twin BD mountings seem not to have been satisfactory, as they were replaced by single 4in guns during the ship’s September 1938 – January 1939 refit. Had war not intervened, Repulse would have been rearmed with seven twin BD 4.5in mountings. Instead, in February 1941 it was proposed to remove all the 4in guns and replace them with seven of the standard twin Mk XIX mountings. Repulse was lost before anything was done. (RAN SPC)
Factors of comparison were shell power, rate of fire and weight of equipment. Shell power (in terms of lethal volume or radius) was based on experiments at Shoeburyness in November 1919. On this basis the 3in HE shell had a lethal radius of about 28ft, the 4in about 37ft, the 4.7in about 46ft, and the 5.5in about 55ft. On the other hand, rate of fire favoured a smaller gun: 20 rnds/min for a 3in, 9.5 rnds/min for a 4in, 5.5 rnds/min for a 4.7in and 3.5 rnds/min for a 5.5in. A gun would probably fire in 10-second bursts, the number of rounds per burst being, respectively, 4.3, 2.6, 1.9 and 1.6. Finally, the weight of a gun mounting and 200 rounds of ammunition could be compared: 4 tons 17 cwt for the 3in, compared to (respectively) 11 tons 3 cwt, 20 tons 19 cwt, and 35 tons 18 cwt. About the same number of personnel (including six to supply ammunition) would be needed for each gun (the 4.7in required more than the others). The Committee tabulated lethal volume (cubic ft) per 10-second burst per cwt of gun and ammunition and per square ft of mounting. Weight was by far the most important factor, and the 3in gun did best, because it fired fastest. The 5.5in did best in terms of deck area, and also in terms of lethal volume per man; but the number of men was the least important factor.
DNO’s BD mounting reached widespread service in the form of the 4.5in Mk II, shown here on board Queen Elizabeth, 2 June 1943. The gun cradles were bolted together, so that they elevated together, as shown. These weapons armed the rebuilt capital ships Queen Elizabeth, Valiant, and Renown, and the armoured fleet carriers. Mk III was a simpler upper deck (UD) mounting. When a dual-purpose destroyer gun was needed in 1941, the BD mounting was the obvious choice. Although it was much heavier than the Mk III, it offered RPC and power loading, the latter important in a lively ship. A Mk II was tested on board the destroyer Savage, and a modified Mk IV mounting developed for the ‘Battle’ class. The 4.5in mounting superseded DNO’s twin 4.7in BD mounting, which figured in sketches of small battleships proposed in 1928. In those it was mounted together with the twin 6in secondaries introduced in the Nelsons.
Another factor was the effect of varying atmospheric conditions as the shell climbed. The heavier the shell (the larger the gun), the less it would be affected. Similarly, a heavier shell would be less affected by wind – and it was unlikely that wind at altitude would be known. The Committee compared the effects of these factors with the diameter of the lethal zone for each shell. It factored in errors in fuse burning (mechanical time fuses were not yet available). An error in fuse timing would have the greatest effect on the shell moving fastest, since that shell could travel furthest during the excess time the fuse burned. The error was also worsened by the spin of the projectile, the 3in and 5.5in spinning slightly more slowly than the others.
The Committee concluded that ‘gun for gun’ the heavier gun was superior on grounds of accuracy and economy of personnel. However, weight the lighter gun from a barrage point of view. The 3in was rejected for its limited range. On the basis of numbers, it seemed that the whole secondary armament of battleships and the main armament of cruisers should be adapted for AA fire. That would leave more space for ‘pom-poms, sound indicators, etc’. In theory a battleship might have some single-purpose secondary guns, ‘but there could be no object in having two different types of gun and mounting of the same