The British Battleship. Norman Friedman

were intended to protect an anchored ship. On 25 May 1915, however, HMS Triumph was torpedoed and sunk during the Dardanelles campaign, even though her nets were deployed. Nets were then abandoned, one argument being that battle damage might put them in the water, where they could foul a ship’s propellers.³⁹

      The full bulkhead consumed considerable weight and it was expensive. Queen Elizabeth had an important advantage: because she burned oil rather than coal, her torpedo bulkheads did not have to be pierced by coal bunker doors. DNC proposed full-scale experiments to test the ship’s protection. First Sea Lord approved the test programme on 13 February 1913. The old battleship Hood was modified to represent the structure outboard of the machinery spaces of a Queen Elizabeth. She was ready in November 1913. Two alternative forms of protection, both involving 80lb (2in) bulkheads, were tried. One, over the engine room, had the bulkhead 7ft outboard of a light bulkhead representing the outside of the machinery spaces. The other, over the boiler room, had the heavy bulkhead inboard and the light bulkhead outboard. In each case the two bulkheads were about 120ft long. In addition to the bulkheads, some compartments outboard of the bulkhead could be filled with oil or left empty. Tests employed 280lb guncotton charges against the ship’s side, 12ft below the waterline.

      The first shot (9 February 1914) tested the thin bulkhead outboard of the thick one. It was blown back against the thick bulkhead, which bulged badly. The outer skin of the ship disintegrated into fragments, the largest about the size of a man’s head. If the compartments inboard and outboard of the torpedo bulkhead were left empty, they perforated the thin bulkhead. When they were filled, the liquid layers protected the bulkhead from the fragments. The inner thin bulkhead successfully resisted the pressure and there was no flooding that a ship’s pumps could not have handled. In a second shot (7 May) the 80lb bulkhead was immediately next to the boiler room, the wing (double-bottom) and outer compartments being filled and the inner compartment next to the boiler room empty. This time the hull was opened over a smaller area. However, the tamping effect of the water in the wing and outer compartment forced the middle bulkhead inwards and broke up the armour shelf at the top of the wing compartment and the hull plating beyond the bilge keel. The light middle bulkhead was driven in towards the boiler room; it tore away from the deck above. The heavy bulkhead resisted the pressure despite bulging inwards. The boiler room sustained only minor leakage.

      These two shots seemed to show that the thick bulkhead should be in the outer position, furthest from the ship’s centreline, to give the innermost bulkhead the best chance of resisting the explosion. It should be strong enough to protect the engine or boiler room from being flooded. The inner (lightweight) bulkhead should be so arranged that any deflection of the heavy bulkhead would not affect it. The question of which, if any, spaces should be filled with oil, water or some solid had not been answered.

      A September 1914 conference reviewed the two test shots and compared conclusions to those reached in the three earlier underwater tests and in the 1913 tests of HMS Terpsichore. It concluded that a series of thin bulkheads would be nearly useless, but that a protective plate (bulkhead) behind a series of filled and empty spaces was best. The bulkheads should be spaced so that the watertight bulkhead inboard of the protective bulkhead would not be affected by the latter’s distortion. The compartment next to the explosion should be empty, to avoid a very destructive tamping or hydraulic effect. The filled compartment (layer) should be next to the protective (torpedo) bulkhead, to protect it from fragment damage. In effect the conference affirmed the design already embodied in the Queen Elizabeth class and a similar system was installed in the Royal Sovereigns – presumably once they had been redesigned as all-oil ships. These conclusions were not far from those the US Navy was then reaching to develop its ‘sandwich’ torpedo protection.⁴⁰

      The experiments implied that existing ships could gain effective underwater protection in the form of an external torpedo protection system: a ‘bulge’ or ‘blister’. It was an external pair of spaces which could be built onto a ship’s hull.⁴¹ The outer space was watertight. The inner was open at the bottom, so that it could fill with water. Inboard of it was the ship’s skin, with a wing compartment (extension of double bottom) at the top. Inboard of that was a coal bunker, with the boiler room inboard of that. The first ships to be bulged were four old Edgar class cruisers, to be modified for shore bombardment. The first British-built monitors were similarly bulged. Work began well before the British lost pre-dreadnought battleships to mines at Gallipoli, but after the mining and loss of the battleship Audacious.⁴² Bulges having proven effective, in 1917 DNC considered installing them on existing ships. The pre-dreadnought Commonwealth was given a bulge similar to that in the Edgars and the coast defence ships Glatton and Gorgon were completed with similar bulges. Two of the Royal Sovereigns were given a ‘girdling’ which, with their existing structure and oil compartments inside the ship, was considered about equivalent to that of an Edgar.⁴³

      The Renowns and the Courageous class ‘large light cruisers’ were designed while the Edgars were being bulged. Their hulls were somewhat bulged out below the waterline to keep a torpedo explosion further from their vitals.⁴⁴ This hull form also reduced draught, which DNC saw as an additional protection (his Minute did not refer to the minimum-draught requirement imposed by Admiral Fisher for his Baltic project). Furious was designed slightly later with a true bulge and a very different structure. Her sloping side above water was carried all the way down to the bottom, the bulge being built outside as a separate compartment. With this outer bulge, the compartments just inside the ship offered total protection which DNC considered equal to that of a bulged Edgar. The same type of protection was incorporated in the Hawkins class cruisers and in the prototype carrier Hermes.

      Given the experience of the Dardanelles, in August 1915 Controller argued that the torpedo menace would continue to be more serious than that of the gun until ship designs incorporated better anti-torpedo protection.⁴⁵ Any new capital ship should have minimum draught consistent with being a practicable seaboat – she must be able to stand the hammering she would receive in heavy weather. He guessed that the minimum would be 20–21ft. Thus future ships would have to be much longer and beamier. Their sides should be bulged below the waterline to keep the centre of any explosion outside the ship. An inner longitudinal bulkhead should be placed far enough inboard to take the pressure of the explosion, preferably curved to the corresponding radius. The ship should have as many transverse bulkheads as possible, to limit flooding and she should have adequate pumping power not dependent on the main boilers. Finally, she should have great freeboard, so that she could survive the considerable list due to an underwater hit on one side. DNC remarked that most of these features were already embodied in the new Large Cruisers (Courageous class and Furious), thanks to Admiral Fisher’s insistence on shallow draught for the Baltic.

      Full-scale experiments were expensive, so in 1915 DNC sponsored a series of experiments to test a proposed scaling law. Given such a law, he could test designs for full-scale protective systems without duplicating them.⁴⁶ The first priority was to develop a means of protecting a fast ship such as a battlecruiser, which could not be given wide bulges. Some shock-absorber was needed. Experiments began at Portsmouth in April 1915 using charges equivalent to 400lbs of TNT. Timber baulks filling the outer part of a bulge wrecked the target. The next shock absorber to be tested was a nest of 3in steel tubes with sealed ends. It appeared that a layer of tubes so absorbed the shock of explosion that the width of the bulge might be halved. This was so encouraging that a full-scale model was built at Chatham, representing half the midship section of a warship, 80ft long and 31ft 6in wide at its bottom, its sides sloping upward and outward. It carried 6in side armour above a bulge. Built in December 1915, this ‘Chatham Float’ was used for full-scale tests up to about 1921. The shape of the float was much like that of the battlecruiser Hood (not yet designed), but with a much thinner belt.

      For many years before the First World War ships carried torpedo nets intended to protect them at anchor. Here the crew of HMS Dreadnought rigs nets prior to a visit from Dominion premiers during a Dominion Conference, probably the one held in 1909. The gauzy