The War Department was the United Kingdom government department responsible for the supply of equipment to the armed forces of the United Kingdom and the pursuance of military activity. In 1857 it became the War Office. Within the War Office the name 'War Department' remained in use to describe the military transport services of the War Department Fleet and the War Department Railways.
One aspect of the War Department's work was the supply of locomotives and rolling stock for use on railways in the United Kingdom, other parts of the British Empire, and in theatres of conflict.
In World War II, large numbers of steam locomotives were produced, as well as some diesel locomotives, of varying gauges to suit the area of planned operation. After the end of the war, these locomotives were largely disposed of to various railways around the world, though some were retained for peacetime use on UK military railways. Of those that were sold, examples of three types ended up as part of the British Railways fleet (where they were often referred to as 'Austerity' locos):
