The War Office was a department of the British Government responsible for the administration of the British Army between the 17th century and 1964, when its functions were transferred to the Ministry of Defence.
The name "War Office" is also given to the former home of the department, the War Office building located at the junction of Horse Guards Avenue and Whitehall in central London. During August 2013 it was announced that the former War Office building would be sold on the open market.
The War Office developed from the Council of War, an ad hoc grouping of the King and his senior military commanders which managed the Kingdom of England's frequent wars and campaigns. It was equivalent to the Admiralty, responsible for the Royal Navy, and the (much later) Air Ministry, which oversaw the Royal Air Force. Its foundation has traditionally been ascribed to William Blathwayt, who on his appointment as Secretary at War during 1684 greatly expanded the remit of his office to cover general day-to-day administration of the Army.
The department had several London homes until it settled at Horse Guards in Whitehall during 1722, where it was to remain until 1858. The War Office was then relocated to Cumberland House, Pall Mall for the last half of the 19th century before finally being relocated to a purpose-built accommodation in what is now known as the Old War Office Building.
The management of the War Office was directed initially by the Secretary at War, whose role had originated during the reign of King Charles II of England as the secretary to the Commander-in-Chief of the British Army. The first War Office Secretary at War is usually said to have been William Blathwayt, though he had two predecessors in the job. It was, however, a fairly minor government job which dealt with the minutiae of administration rather than grand strategy. Issues of strategic policy during wartime were managed by the Northern and Southern Departments (the predecessors of today's Foreign Office and Home Office).