For example, in 1940–1 the US Navy ran simulated torpedo attack exercises, the attackers’ tactics being modelled on those demonstrated during the ongoing European war. The attackers flew a course parallel to that of the ship and then turned suddenly towards the target, glided down to attack height (diving at an angle of 15° to 30°), and released their (notional) torpedoes. One US cruiser captain pointed out that such tactics would place the burden of defence on the only guns which could bear along the ship’s centreline, the newly installed 1.1in machine cannon. If he tried to unmask his main anti-aircraft battery of 5in guns he would present his broadside to the attackers, much simplifying their task. The perception of this problem probably explains why the US Navy chose to place two single 5in guns on the centreline of its last pre-war heavy cruiser (Wichita) and why the new cruisers it designed in 1939–40 (Clevelands, Brooklyns and Alaskas) all had twin 5in guns on their centrelines, fore and aft.
Guns
The guns in this book may be characterised as quick-firing (QF in British terminology, RF in US), semi-automatic, and automatic. Both QF and semi-automatic guns fired one shot at a time; they had to be reloaded between shots, and the gunner had to pull the trigger (or some other firing device) for each shot. Automatic guns fired continuously, as long as the firing device was engaged and ammunition lasted. All of these guns used brass cartridge cases, because it was impossible to load a gun with bag ammunition at high elevations. In this regard what mattered about the cartridge case was that it was rigid.
Firing at a high angle, a gun had to have enough space under it to recoil. To do that, its mounting had to have its trunnions, about which the gun elevated, as high as possible. That in turn made it difficult to load the gun when it was at a lower elevation. High-angle targets also complicated sight design, because the gunner ideally could stand or sit while aiming. This 3in HA gun is on board a British First World War battleship. Note how far down the loader has to kneel. Some inter-war Italian medium-calibre mountings were designed to raise their trunnions as the gun elevated, so that it could be loaded equally easily at high and low angles.
Cartridge cases also made it possible to use simple quick-acting breech mechanisms, because when the gun fired the case expanded to help create a gas seal. The case then quickly contracted as it cooled, so it could easily be extracted. In a QF gun, extraction was done manually. A semi-automatic gun used the recoil energy of the gun to eject the cartridge case and to prepare the breech for the next round. That made for faster fire. Semi-automatic guns existed in small numbers during the First World War, but became common afterwards. The US Navy’s 5in/38, its standard heavy anti-aircraft gun of the Second World War, was a typical semi-automatic weapon. Movies of anti-aircraft action make it obvious that the gun threw out its spent cartridge cases upon recoiling.
Automatic guns take the process a step further, using the energy of firing not only to eject a cartridge and to recock the firing mechanism, but also to reload the gun and then fire again. The two main sources of energy for all this are the gun’s recoil and the gas produced when the gun fires. For example, the widely-used Bofors 40mm gun was recoil-operated. As the gun recoiled, it compressed a heavy spring wound around its barrel (and very visible in photographs). The spring returned the gun to firing position, and the energy of the recoil was used to eject, reload, and recock.
The energy of recoil or gas is limited, so it is not possible to produce a fully-automatic gun above a particular calibre (the limit is probably about 57mm, as in the post-1945 Bofors replacement for the 40mm gun). Larger weapons can eject and reload automatically, but it takes external power to supply rounds to the breech. Work on such powered automatic guns seems to have begun before the Second World War, and the first such weapons appeared at the end of the war. The first US example was the power-operated 3in/50, which was the earlier semi-automatic gun with a power loader and a slightly modified breech. One of the less happy lessons of post-war anti-aircraft development was that power-loading systems often jammed, and that gun mountings had to be de-rated (slowed down) if they were to function effectively. An alternative approach was to abandon really heavy anti-aircraft calibres in favour of smaller rounds more amenable to power operation.
The US Navy’s solution to the trunnion-height problem was to place the gun on an elevated platform, like that shown on this 5in/38 aboard the carrier Yorktown, at Newport News (newly completed) on 27 September 1937. Loaders on the platform could easily load the gun at any elevation. The structure in the foreground is the fuse-setting machine; loaders moved shells onto the platform, placed them nose-down in the machine (three at a time), then withdrew them and loaded them. The Royal Navy disliked this solution for high-powered destroyer guns, presumably because it raised the centre of gravity of the gun mounting. Much of the structure visible around the breech of this gun is a massive counterweight, moving the centre of gravity of the gun so that its trunnions can be placed nearer the breech, limiting the necessary trunnion height. The Germans went furthest in this direction, their trunnions being nearest the breech, and their barrels elevating through the roofs of their gun houses.
This book is about the gun defence of surface ships, but fleet air defence also involved fighters, both carrier- and land-based. Situations alternately favoured or precluded much fighter air defence of ships. Throughout the war, it seems to have been clear that fighters and guns were complementary, but that guns could never exact enough of a toll on attacking aircraft to end the problem. It seems clear that guns tended to beat off attacks and to shake attackers sufficiently to ruin their aim, thus saving ships. That was much the lesson the Royal Navy much later drew during the Falklands War of 1982, when surface defences, fighters and attackers were all much effective than they had been during the Second World War.
Another solution to the trunnion-height problem was to provide a pit into which the gunner could move as he elevated his gun. The Royal Navy tried this solution in a HA destroyer mounting in the 1920s, but disliked it for its complexity. Portable deckplates had to be provided for gunners when the gun was at a shallow elevation. Aside from that, opening the main deck of a small ship to provide such a pit cut into the ship’s girder strength. This 20mm Oerlikon is on board the Canadian armed merchant cruiser Prince Robert. (RCN)
Some designers overcame the trunnion height problem by detaching the gunner from the guns, giving him a separate sight which he could use while standing. This quadruple Vickers 0.5in gun was aboard HMAS Perth. Unlike the Oerlikon, it was not free-swinging; the gunner turned the mounting with his body, but he elevated using a wheel and gearing. It turned out that a gunner could manipulate a free-swinging mounting, like that of the Oerlikon, much more easily than he could manipulate his wheel. During the Second World War the US and Royal Navies both devised one-man controls for powered anti-aircraft mountings, replacing separate pointer’s (in British parlance, layer’s) and trainer’s wheels. The wartime ones were called ‘scooters’, because their horizontal bars resembled the handlebars of scooters. After the war the US Navy preferred joysticks. In each case, it was vital to find a mechanism a gunner could handle intuitively. (State Library of Victoria)