By the late 1930s the British were well aware of the advantage of this kind of control, to the point where they considered anti-aircraft control without it useless at short ranges, where gun mountings had to turn very rapidly. The British termed the systems involved Remote Power Control (RPC), and developed several types denoted by RP numbers.
The Germans used a form of RPC based on magnetic amplifiers rather than vacuum tubes. The US Navy’s Bureau of Ordnance found magnetic amplifiers particularly interesting, and it used them in at least one aircraft fire-control system.
A quadruple 40mm gun is shown in action on board the battleship West Virginia, 22 July 1944. The smaller splinter shield above and on the right side of the main gun tub contains a Mk 51 director controlling the gun mount. Although the trainer and pointer are in their seats, the mount is fully controlled by the Mk 51, training and elevating under power. Note the telephone head set worn by the Mk 51 operator. Although the director was wired directly to the gun mounting, its operator received target designation information by sound-powered phone from the ship’s Combat Information Center. This was standard US practice.
Saturation
Only towards the end of the inter-war period did navies apparently begin to face the problem of multiple attacks against one ship. It was one thing to concentrate a ship’s fire using a single director-controlled system focussed on a single attacker. It was another to recognise that an intelligent enemy would try to attack at least from both sides of a ship. To some extent barrage fire was a means of handling massed attackers approaching from roughly one direction.
No one used modern terms such as ‘channels of fire’ or ‘saturation’, but they were the issue. One US Navy approach was to estimate the unit of fire necessary to engage a single aircraft with a reasonable chance of success. At one time that was four 5in guns backed by one fire-control system. In theory, each unit of fire represented a channel of fire (the ability to deal with one target), although in practice a ship would be unlikely to be able to bring all her channels of fire to bear against an attack from one side. As the number of attackers mounted, there was a strong temptation to split up a ship’s anti-aircraft battery as finely as possible. For example, in 1943 the US Navy decided to assign a short-range director to each 5in mount. That did not change the statistical character of anti-aircraft fire: the fewer the guns firing at an aircraft, the less the chance of shooting it down.
Both the US Navy and the Royal Navy liked open anti-aircraft mountings, on the theory that the gunner needed a clear overhead view as a backup if director control failed. That did not allow for splinter or strafer protection, and during the war such guns were increasingly shielded. This 4in Mk V gun was on board an Australian cruiser; the crew is shown at action stations. The large disc on the left-hand side of the gun is the fuse dial. Note the angled eyepieces for the layer’s and trainer’s telescopes, on either side of the gun, so that they did not have to squat as the gun elevated to track a HA target. Note the fixed 4in round held by the loader. It was about the largest single item of ammunition which a man could quickly load. The US 5in/38 had semi-fixed ammunition, with shell and cartridge separate so that they could be handled easily. The fuse-setting machine is on the platform on the left side of the gun (a shell is being inserted into it). Note the handle: the fuse machine operator turned it to match a dial setting transmitted by the fire-control system. (State Library of Victoria)
Placing Guns
Somewhere else in the equation was the choice and placement of the guns and fire controls, which varied considerably from navy to navy, and the relation between guns and fire controls. Placement was chosen both for tactical reasons and due to the limitations set by ship real estate. For example, it was generally much easier to place anti-aircraft guns on a ship’s sides than on her centreline. The best centreline positions were occupied by a ship’s main battery, generally of anti-ship guns. Bridges and machinery occupied most of the remaining usable centreline of the ship. On the other hand, aircraft might often attack from ahead or astern, flying down the length of the ship. Some of the guns might bear, but a ‘sided’ battery would find it particularly difficult to track an aircraft crossing the ship’s track. That applied not only to the guns but also to their directors.
A ship’s captain had to balance his manoeuvring choices in the knowledge of the arcs of both directors and guns. He might find it difficult to turn so as to unmask the battery on one side, because that might make the bombers’ task easier. The ship would present a larger target. How important that was depended on how the captain judged the relative threats presented by level, dive, and torpedo bombing. Level bombers might prefer to fly down the ship’s hull, because they were more likely to err in range than in line (in reality they tended to spread their bombs both ways). Dive bombers could attack from any direction, because they were relatively accurate. A torpedo bomber preferred to attack more or less abeam, because range errors line were insignificant compared to errors in line (bearing).
It took a combination of light and medium-calibre anti-aircraft guns to protect a large ship under air attack, but she might be fighting a surface action at the same time. The Japanese seem to have been alone in providing blast shields for their light anti-aircraft guns. This photograph was taken on board the super-battleship Musashi when the Emperor visited on 24 June 1943. At upper centre is one of her shielded triple 25mm mounts, the shield being about the size of that of a 12.7cm gun like the ones visible on the right. Note that the 12.7cm shields are considerably more streamlined (and more complete) than those on board other Japanese warships, possibly as an anti-blast measure. The photograph was taken on the ship’s port side, looking aft. When the ship’s anti-aircraft battery was upgraded with many more 25mm guns, the anti-blast shields were apparently no longer in production, so the additional guns were unshielded, like all others in Japanese naval service.
The obvious place to put anti-aircraft guns is on the sides of the superstructure, but that makes it easier for an attacker to fly down the centreline of the ship. When it designed new cruisers, unconstrained by treaty, from 1939 on, the US Navy adopted a new arrangement including centreline 5in guns, as shown by Pittsburgh off Boston on 1 November 1944. It is not clear whether the designers were trying to increase end-on firepower or were forced to place the mounts on the centreline because there was no other space along the ship’s length. The evaluation by the immediate post-war Pacific Fleet board on wartime ordnance experience (the Kraken Board) favoured the latter explanation, and argued further that the centreline positions exposed control positions to excessive gun blast. On the other hand, the US Navy was probably unique in placing its long-range anti-aircraft directors on the centreline, where they could follow a target across the ship’s beam. Late pre-war exercises against simulated torpedo bombers certainly demonstrated that ships lacked the ability to handle such targets.
Savannah is shown as rebuilt after battle damage by a German guided bomb at Salerno in September 1943. The line of her blister is evident roughly abreast No 4 turret. The new gun mounts were controlled by new Mk 37 fire-control systems. Clearing the sides between the mounts left space for more Bofors guns. She had four quadruple mounts and six twin mounts (two on her quarters are hidden by her catapults), a total of twenty-eight guns.
Gun placement could have subtle implications. With a total of five main-battery turrets, the Brooklyn class cruisers had their batteries of four 5in/25s on each side squeezed into a smaller space than on the previous New Orleans class heavy cruisers. When the ships entered service, it turned out that their