During the First World War DNC conducted extensive scale model tests of alternative forms of underwater protection, finally building a full-scale model (the ‘Chatham Float’, shown here) for proof tests.
By the end of the war, there was a real question as to whether underwater protection was worth its considerable cost in terms of ship volume. There was no obvious limit to the explosive load torpedoes could carry, particularly if they were filled with new explosives such as Torpex. Internal volume had always been a problem. During the design of the abortive 1945 battleship, it was seriously suggested that conventional underwater protection be abandoned altogether. Carriers were a different matter, since their beam was set by flight deck dimensions, so they were able to accommodate wide side-protection systems.
As work on a new battleship began in 1944, another underwater protection question was raised. Since the Nelsons, the magazines in new battleship designs had been placed below shell rooms to protect them against diving shells. Battleships now faced influence mines and non-contact torpedoes which exploded under them. Was the previous practice still valid? The answer was needed urgently, because the design of the new turrets, the controlling factor in building a battleship, depended on it. DNC considered it unlikely that an under-bottom explosion would ignite a magazine. With the advent of guided bombs such as the German FX-1400 (which had nearly sunk HMS Warspite and had sunk the Italian Roma) the case for keeping magazines below shell rooms seemed stronger than ever. Trials with a mine filled with Amatol had shown that although some cordite might ignite, the inrush of water would quench the fire. However, some escorts seemed to have suffered magazine explosions after having been torpedoed. The Germans used torpedoes with a quarter aluminium filling for greater flash and heat. However, an aluminised explosive such as the Germans used might cause a considerably larger fire. US experience with the cruiser Savannah, which suffered a hit in a magazine by a German guided bomb, was encouraging: there was no serious powder fire or explosion. That suggested a cure other than modifying the location of the magazine.
Small-scale trials, which were continuing, were not considered sufficiently representative of the full-scale situation. In August 1944 the disabled battleship Warspite was proposed for a full-scale trial.55 Warspite had her magazine above her shell room, so ‘B’ shell room and ‘B’ magazine would be stripped out, each rebuilt to represent the other function. The ship would be made watertight and her reserve of buoyancy increased to reduce the chance of a total loss which would destroy important evidence of what had happened. Even a total loss would answer the question of whether water would rush in quickly enough to extinguish the fire or the rate of burning (of cordite) would increase so quickly that the magazine would explode. DNO argued that such a trial would have a far-reaching effect, determining capital ship magazine arrangements for many years to come. Plans called for detonating 750–1000lbs of aluminised explosive 3–4ft under the ship’s bottom. Plans for the full-scale trial seem to have died at the end of the war; Warspite was never tested.
The Royal Navy also devised tactics to evade a torpedo salvo, particularly one fired by the enemy battle line. The C-in-C maintained situational awareness using a plot and he could signal a group turn to evade expected torpedoes. That was the basis of the turn-away at Jutland, based on Admiral Jellicoe’s plot. After the battle, there was considerable interest in different torpedo evasion tactics. One observation was that not all of the British battleships might be threatened. Although the C-in-C retained the option of ordering all the ships in the battle line to turn away (or, later, towards) the enemy to comb torpedo tracks, ships’ captains were also given the option of individually evading. To make that practicable, ships were given enclosed torpedo lookout positions, typically on the foremast (in a few cases, on either side of the bridge structure). These boxes are the visible indications of a radical change in Grand Fleet tactics. After the war the much less numerous British battle fleet adopted more widely-spaced formations, which in themselves made ‘browning’ shots by an enemy battle line much less profitable. The enclosed torpedo lookout positions were gradually eliminated.
Fuel
By the time HMS Dreadnought was built, the Royal Navy burned coal but was using oil either as a supplement (to be sprayed on the coal fires in boilers) or as a future single fuel.56 From 1904 on, all large new ships were designed to burn some oil as well as coal. The new coastal torpedo boats (‘oily wads’) and ‘Tribal’ class destroyers were designed to burn only oil. Boilers in large ships were designed to develop full power on coal, oil being sprayed on as a means of increasing endurance of fuel and personnel and also as a means of quickly increasing and maintaining maximum power. By 1908 there was some question as to whether the supply of oil could be assured, so the Beagle class destroyers reverted to coal-burning. Their design made the limits of coal so obvious that all subsequent British destroyers burned only oil. The follow-on Acorn had a more powerful armament on 20 per cent less displacement, cost 16 per cent less and was 1.5 knots faster and unlike a coal-burner she could maintain her speed until her fuel ran out.
In Wales the Royal Navy had an excellent supply of the best steaming coal in the world. However, coal had had to be shovelled manually into the boiler face. Each boiler therefore needed an accessible face and human limitations on shovelling limited the size of the boiler. The space in front needed access to coal bunkers. Coal in distant bunkers had to be moved manually (‘trimmed’) into position closer to the furnaces. This was so significant a limitation that when the battle-cruiser Invincible made a celebrated transatlantic run (at an average of 25 knots) in 1909, holes were cut in bulkheads to provide better access. At the very least, the need for access limited a ship’s watertight integrity. No matter how good, coal left ashes and other solid refuse (clinker), which had to be cleaned out periodically, dramatically reducing a ship’s continuously available power and thus slowing her down at what might be a crucial moment. Typically a coal-burning ship could maintain full speed for a distance equivalent to 60 per cent of her fuel capacity. Coal had to be loaded into bunkers by hand, typically from bags delivered to a ship’s deck. Coaling was an all-hands evolution, laborious and filthy. A ship’s company had to move hundreds of tons of coal per hour. Although the Royal Navy (and the US Navy) expended considerable effort to develop mechanical means of coaling at sea, that was never an easy process.
Oil offered 1.3 to 1.4 times the thermal content of the best coal: a given weight of oil would drive a ship further.57 Moreover, coal deteriorated in storage (at bases it often had to be stored under water) and its quality varied enormously from place to place. Coal also took up more space per ton, because it was not a solid mass like the oil in a tank: typically 40–43ft3 vs 38ft3 for oil. Oil bunkers could be filled to 95 per cent, whereas space had to be left at the top of coal bunkers for ventilation and for access. During the First World War many ships found that the large amount of coal in their reserve bunkers was effectively unusable. Writing in 1937, a senior British naval engineer particularly cited HMS Agincourt, whose three boiler rooms had, respectively, about 450, 800 and 2000 tons of coal around them. She was converted to burn 600 tons of oil during the first six months of the war. Had this not been done, she would have been unable to keep operating at sea after a few days at high speed, because her endurance would really have been set by the 450 tons in the first boiler room. Advocates of coal pointed to its protective value, but the coal in the upper bunkers, which might offer protection, had to be burned first, to maintain stability and to afford an adequate supply to the boilers. By the time the ship fought,