The War Department was the government department responsible for military activity and the supply of equipment to the British armed forces. It was originally established in 1794, when the position of Secretary of State was created. Over the years it has been known by a number of different names, these include the Colony Department, Colony and War Department, Colonial Department and the War Office. Today it is known as the Ministry of Defence.

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.