The British Battleship. Norman Friedman
be gone and it might be further compromised by a bunker door jammed open with coal.
An oil-fired boiler did not require an open stoking space in front of it, nor was its size limited by what one stoker could shovel into it. It also did not require very many personnel. These considerations made oil so attractive that before the First World War the Royal Navy shifted to all-oil burning for light cruisers. An incidental advantage was that fuel supply to boilers could be switched on much more rapidly than with coal-fired boilers. At Heligoland Bight in 1914 the Germans found that British destroyers and cruisers accelerated much faster than their coal-fired ships. On the other hand, it was feared that a hit on an oil bunker would start a fire; since oil would float on water, it would be difficult to extinguish. At least before 1914, the Royal Navy therefore stowed its oil fuel only in bottom tanks. Only much later did it accept the idea that oil fuel could function as a liquid load in side (underwater) protection.
Up to the Royal Sovereign class, British capital ships, including the Queen Elizabeths, were designed to burn coal.58 Conversion (at the design stage) of the Queen Elizabeths seems not to have bought greater power output. The modification of the Royal Sovereigns seems to have been the first time advantage was taken of the superior efficiency of oil fuel, power output within a fixed volume increasing by a third. The Renowns were designed to use existing boilers modified to burn oil. Hood was designed from the outset to burn oil. That explains why she had twenty-four boilers producing about 50 per cent more power than Renown’s forty-two: the limit on boiler size imposed by coal-burning had been eliminated. The shift to smaller numbers of much larger oil-burning boilers explains why one boiler room in the rebuilt Queen Elizabeths could be eliminated altogether. Adopting oil fuel offered a dramatic reduction in engine-room personnel: Tiger needed 600 for 108,000 SHP (mixed firing), but Hood (144,000 SHP), needed only 300 for her all-oil powerplant.
For the Royal Navy an additional consideration was that oil had to be imported from overseas. That became a real problem during the U-boat offensive of 1917–18. In 1931 a petition was raised to revert to coal fuel, the argument being that mechanical stokers using pulverised coal had changed the situation.59 In 1938 retired Captain Bernard Acworth published a book, Britain in Danger, arguing that Britain could regain naval supremacy by, among other things, reverting to coal fuel. DNC was compelled to estimate the cost of reversion.60 It included the cost of converting all available spaces abreast the boilers for coal stowage, provision of shovelling flats, sloping chutes and special hatches, as well as supply and exhaust ventilation (coal dust could burn or explode). DNC concluded that Hood would be impossible to convert. The Nelsons, designed for oil fuel, would cost £50,000 each, as would each Royal Sovereign. Queen Elizabeths would cost £60,000 each. Worse, ships would accommodate a smaller tonnage of coal than their current oil supplies, since oil could be stowed over much larger spaces in a ship. Given the greater thermal content of oil, steaming radius would be far shorter.
Gunners relied on searchlights to see their targets at night and considerable effort was devoted to developing the right lights and also into placing them. HMS Neptune shows her double 24in searchlights, the pre-war standard. Note that this photograph was taken before rangefinders were installed in her ‘X’ and ‘Y’ turrets.
During the First World War the controlling factor in the endurance of the Grand Fleet was the endurance of its destroyers. Before the war, it had been expected that destroyers would conserve fuel, steaming out to rendezvous with the fleet when action was expected. That was never really practical. Because British destroyers burned oil, it was possible to fuel them from the capital ships; the British developed the towed-astern technique for this purpose.
Note that, unlike reciprocating engines, turbines could absorb far more than their rated power in terms of steam. Ships were often rated at both normal and overload output, the difference being the extent to which boilers were forced. Note too that until about 1910 it was impossible to measure turbine output directly, as the output of a reciprocating engine could be measured (indicated horsepower, IHP). Naval architects could certainly measure the effective horsepower (EHP) required to move a ship at a given speed and they were well aware that propellers typically translated about half their input power into EHP. Therefore for some time the Legends of British capital ships show a requirement for turbine power equivalent to a given IHP. This is often quoted as SHP, but that is misleading. For example, initially turbines were far less efficient than reciprocating engines because they turned propellers at higher speeds. Moreover, attempts to produce turbines turning at more efficient speeds translated into much larger (longer) turbines. Another problem was that a turbine could not be throttled down efficiently; it had only one (high) efficient speed. The solution to the turbine speed problem, introduced during the First World War, was to gear down a faster-running turbine. The solution to inefficient operation at lower speeds was cruising turbines.
THE APPROACH TO THE DREADNOUGHT REVOLUTION
HMS Dreadnought combined a new kind of main battery – all big guns – with a new standard of strategic mobility achieved using steam turbines. The change in battleship armament was already in the air when Dreadnought was built; she merely accelerated it. Steam turbine mobility may have been the more shocking achievement.
Between about 1890 and 1900, a standard type of battleship emerged, armed with four heavy guns in twin mounts, a battery of ten to fourteen quick-firing guns of roughly 6in calibre, lighter anti-torpedo (boat) guns and torpedo tubes, plus machine guns which could be used against exposed enemy personnel at short battle ranges. Initially the logic of such a design was connected with the nature of battleship armour. It took very thick, hence very heavy, armour to resist the most powerful shells. A ship of affordable size (12,000–14,000 tons) could not carry much side armour beyond a waterline belt, which was associated with a protective deck. In battle, the slow-firing heavy guns (firing a shell every few minutes) would attack the belt and thus the ship’s vitals. The quick-firing guns, of roughly 6in calibre, would attack the unarmoured side of the ship.
At the battle of the Yalu in 1894, Japanese cruisers armed with quick-firing guns overwhelmed Chinese battleships protected only against heavy but very slow-firing guns. Many naval officers now argued that medium-calibre quick-firing guns could overwhelm battleships, particularly those whose armour was limited to a heavy waterline belt. As C-in-C Mediterranean from 1899 to 1901, Admiral Fisher added another argument. He considered it suicidal to close to within enemy torpedo range, which he thought would soon reach 3000 yds (it would already reach that in a stern chase). On this basis he argued that ‘the armament we require is the greatest number of the largest quick-firing guns in protected positions. They call it the secondary armament; it really is the primary armament’.1 Fisher argued that slow-firing heavy guns were useless against fast-moving ships; they were ‘as obsolete as the foot soldier in the Boer War’. In his view, the decisive phase of battle would be the destruction of the entire unarmoured part of an enemy ship by 6in quick-firers hitting from outside enemy torpedo range, at ranges perhaps as great as 5000 or 6000 yds. At this time the standard range for prize firings was 1400 to 1600 yds and Fisher wrote elsewhere that he wanted to fight at 3000 to 4000 yds. Any approach inside 2000 yds would invite torpedo attack (or within 3000 yds in a stern chase). At this point guns were still individually aimed, although Fisher had initiated fire-control experiments leading to salvo fire and to concerted fire control. Thus his Mediterranean Fleet papers included a table of hitting probabilities at various ranges. The table showed that a numerous fast-firing 6in battery had an excellent chance of hitting at the extended ranges he had in mind. It is no surprise that initial British attempts to improve battle range (about 1901) focussed not on the heavy guns (in theory the main battery) but on the quick-firing ones.