Fuel

The first generation of dreadnoughts used coal to fire the boilers which fed steam to the turbines. Coal had been in use since the very first steam warships, but had many disadvantages. It was labor-intensive to pack coal into the ship’s bunkers and then feed it into the boilers. The boilers became clogged with ash. Coal produced thick black smoke which gave away the position of a fleet and interfered with visibility, signaling, and fire control. In addition, coal was very bulky and had comparatively low thermal efficiency. Coal was, however, quite inert and could be used as part of the ship’s protection scheme.[81] Oil-fired propulsion had many advantages for naval architects and officers at sea alike. It reduced smoke, making ships less visible. It could be fed into boilers automatically, rather than needing a complement of stokers to do it by hand. Oil has roughly twice the thermal content of coal. This meant that the boilers themselves could be smaller; and for the same volume of fuel, an oil-fired ship would have much greater range.[81] These benefits meant that, as early as 1901, Fisher was pressing the advantages of oil fuel.[82] There were technical problems with oil-firing, connected with the different distribution of the weight of oil fuel compared to coal,[81] and the problems of pumping viscous oil.[83] However, the main problem with using oil for the battle fleet was that, with the exception of the USA, every major navy would have to import its oil. This meant that a number of navies adopted ‘dual-firing’ boilers which could use coal sprayed with oil; British ships so equipped, which included dreadnoughts, could even use oil alone at up to 60% power.[84] The US was a major oil producer, and the U.S. Navy was the first to wholeheartedly adopt oil-firing, deciding to do so in 1910 and ordering oil-fired boilers for the Nevada class, in 1911.[85] The United Kingdom was not far behind, deciding in 1912 to use oil on its own in the Queen Elizabeth class;[84] shorter British design and building times meant that Queen Elizabeth was commissioned before either of the Nevada class. The United Kingdom planned to revert to mixed firing with the subsequent Revenge class, at the cost of some speed—but Fisher, returned to office in 1914, insisted that all of the boilers should be oil-fired.[86] Other major navies retained mixed coal-and-oil firing until the end of World War I.[87]