than coal, allowed larger and faster warships, and being easily piped, was easier to supply to ships at sea. By the start of World War I, both the Queen Elizabeth-class and the Revenge-class battleships were partly oil-fired: oil was used mainly for both quick-start steaming, and sprayed on burning coal to extend their range. A number of cruiser and destroyer classes produced since 1904 also used oil. However, by the time of the Battle of Jutland in May/June 1916 still only a sixth of the Grand Fleet was oil-fired. Further, that summer the British suffered a number of losses of oil tankers, and had to instruct oil-fired ships to restrict their fuel consumption and hence speed. When the United States entered the war in April 1917, the British instructed the United States Navy to send only coal-fired ships to assist them. To assist the Royal Navy, from the outset of the war the Government and railway companies ran what were termed "Jellicoe Specials", high-speed coal carrying freight trains that ran from South Wales to north-east Scotland, and then by ship to Scapa Flow. Initially running to Dingwall, they then were also shipped to Scrabster through Thurso. However, inadequate capacity in port and rail facilities at these locations meant that from January 1915, all naval ordnance (other than ammunition) and medical supplies were sent by rail to Aberdeen, and from mid-1915 Grangemouth. By the end of WWI, the Royal Navy had 33 dreadnoughts and 9 battle cruisers, with 10 and 2 respectively entirely oil fuelled. However, after WWI, the move to oil-firing was quickly extended to other areas, including the railways, which was a key strategic factor in the economic hardship which struck the coalfield after the war. Coal workings were over-expanded in the late nineteenth century, and the Welsh coal owners had failed to invest in mechanisation. By the inter-war period the South Wales Coalfield had the lowest productivity, highest costs and smallest profits in Britain. Hardship continued through the 1926 general strike, the great depression of the 1930s, World War II and thereafter. The 1937 novel The Citadel and the 1939 novel How Green Was My Valley (later filmed, with a wildly inaccurate "colliery village") describe such hardship, as do the poems of Idris Davies the miner, teacher and poet of Rhymney. New collieries, particularly in the western part of the coalfield where anthracite is found, were developed into