The British Battleship. Norman Friedman
normally carried rolled up against the ledge visible on the side of the ship. Once unrolled, it is spread over the heavy line visible just below the ledge, which in turn runs between the upper ends of the booms lashed diagonally to the hull. The booms could then be lowered to create a curtain around the ship. By 1914 it was not at all clear that nets would be effective in the face of net-cutters normally mounted on torpedoes and there was a real fear that if they were damaged in action they would foul a ship’s propellers. Moreover, the strategic situation left few ships anchored in exposed places. One of the exceptions was HMS Triumph, sunk at anchor in May 1915 despite her nets.
A 400lb charge exploded 15ft below the waterline made a hole about 15ft in diameter in the outer plating of the bulge. Its force was almost completely absorbed by a nest of closely-packed 9in steel tubes forming a layer between an outboard void and a bulkhead representing the outside of the ship’s vitals. The simulated ship’s structure was almost undamaged. This type of protection was incorporated in the monitors Erebus and Terror and in HMS Hood. Also in 1915, the decision was taken to incorporate this type of protection in the battleship Ramillies, then under construction. DNC was proud that careful design had limited the cost (in speed) of this bulge to a quarter-knot. Overall, bulging could allow capital ships to meet torpedo fire in much the same way that they met gunfire with their armour.
The question was whether the Royal Navy was justified in not bulging all its capital ships. On 29 August 1918 the Board referred the question to a committee headed by Admiral Jellicoe, the other members being Controller, Fourth Sea Lord and DNC, with Captain F C Dreyer as secretary. C-in-C Grand Fleet (Admiral Beatty) asked to attend when possible and Jellicoe asked that a torpedo officer (Commander M K Grant) be added as a second secretary. On 4 November 1918, the committee recommended that all new capital ships have bulges about 400ft long, sufficiently strong to resist two 21in torpedoes. It envisaged an area of damage 20 to 30ft long. As an example of what could be done, DNC had reported that under certain conditions and with torpedoes spaced 60ft apart, Hood could continue underway after being hit by eight torpedoes with 600lb charges. All battleships from the King George V class onwards and battlecruisers from the Lion class and the carrier Eagle should be bulged. In the case of the Queen Elizabeths, it should be a matter for the Board as to whether a loss of three-quarters of a knot could be accepted ‘in view of the known speed of the later German battleships’.47 The Board had recently approved bulging the two Renown class battlecruisers and that in turn had delayed the planned ‘girdling’ of the last two Royal Sovereigns.48
With the war over, in February 1920 DNC pointed to the high cost of bulging the existing obsolescent ships. A major consideration, which DNC and the Board did accept, was that larger floating docks would be needed to accommodate bulged ships.49 Ultimately the decision was to bulge the remaining 15in gun battleships – two Royal Sovereigns and the Queen Elizabeths – which would be the core of the post-war fleet.
It proved impossible to repeat DNC’s favoured Hood arrangement in the post-war capital ships. Hood had incorporated sloped armour to provide sufficient protection, but the ships designed in 1920–1 and afterwards had to be protected against more powerful shells at greater ranges. For that their designer adopted more steeply sloping armour, which could not be placed outside the hull.50 That in turn required that underwater protection be internal. In line with his criticism of US underwater protection, DNC also was concerned that the internal protection system be designed to vent the gas of any explosion outside the protected citadel. He ended up with a series of steeply-sloping bulkheads reinforced with tubing. The Chatham Float was modified to test it against a 750lb charge.
The same underwater protection was incorporated in the O3 design which became the Nelsons. It was realised that the arrangement of belt armour and the underwater protection system, adapted from the previous design, were too closely related to separate.51 DNC cited quarter-scale underwater tests which showed that decreasing the slope of the belt would jeopardise underwater protection. These models represented the planned O3 protection, a modified version of O3, the American system of vertical bulkheads in a ‘sandwich’ (as understood from wartime data) and a modified American system. All were tested against the equivalent of a 1000lb torpedo warhead. The O3 design performed best, the modified British system being inferior. To offer the same resistance as the British system, the American system had to be made about a quarter heavier. Even then DNC considered it distinctly inferior. Weight was particularly important for ships designed under the Washington Treaty displacement limit. The tests appeared to show that arrangements to vent the water jacked (and, in future, the air jacket outboard of it), which were embodied in the British but not the American systems, were necessary to limit damage to the ship proper. In the American systems the outer bottom was forced down the equivalent of 3ft in a full-scale ship. DNC pointed out that such damage might make it impossible to dock such a ship promptly for repairs.
DNC felt vindicated and the Board confirmed the O3 design.52 However, some changes were made. The belt was brought out to the side of the ship, to reduce any gap into which a shell might pass. Its slope was reduced from 18° to 15° slope for the same reason. The main deck was given a slight slope, as in G3 and the belt slightly reduced in height.
The resulting combination of deeply-sloping side armour and sloping underwater bulkheads was incorporated in the designs for abortive battleships drawn up during the 1920s. However, by the time the British were designing a new battleship in 1933, they had shifted to a US-style sandwich of vertical bulkheads with an outboard air space, a liquid layer and then an inboard air space. At the same time the inclined internal belt of earlier designs was dropped in favour of an external vertical belt. Although quite different in detail, this was broadly the US system of protection which DNC had considered inadequate a decade earlier. Ironically, the US Navy adopted a British-style internal inclined belt for its South Dakota class in 1936, because that was considered the only way to obtain sufficient protection (against 16in shellfire) within treaty-limited displacement.
HMS Thunderer shows the torpedo net booms, pivoted at their lower ends. The net itself, normally stowed along the deck edge, is not present.
Active protection against torpedo boats and destroyers was broadly analogous to later protection against air attack. Until 1910 the British assumed that destroyers would attack at night, so torpedo defence guns could be mounted on turret tops (as well as in superstructures). These 4in/45 guns were photographed on board HMS Invincible when she visited New York City in 1910 for a naval review, after a celebrated maximum-speed dash across the Atlantic.
The new British system was based on small-scale experiments, but adoption was also connected with efforts to protect against diving shells, a threat revealed in firing experiments against the battleship Emperor of India. It was first used in the carrier Ark Royal and then in the King George V class. Having been adopted, the new system was tested successfully against 750lb charges in a new full-scale device called Job 74.53 The Royal Navy thus began the Second World War convinced that it had mastered the torpedo problem. The loss of both Ark Royal and Prince of Wales to torpedoes, in the latter case with considerably smaller charges, was therefore particularly shocking. In both cases a special committee of outside experts (First and Second Bucknill Committees) was formed to review current underwater protection. It turned out that in each case the torpedo protection system had not really been tested. Ark Royal was hit at the turn of her bilge as she turned sharply to evade torpedoes. Even though the hit defeated her side protection, she could have been saved had she been counterflooded properly (it did not help that she lost all power). Prince of Wales suffered an even more unfortunate hit, which caused widespread flooding through her outboard port shaft alley. Nothing in the ship’s side protective system would have solved the problem.
By 1944 the Admiralty Underwater Experimental Works (UNDEX) was testing models of the underwater protection for the large carriers then planned. It was also conducting small-scale