The name 'Old War Office' is also given to the former home of the department, located at the junction of Horse Guards Avenue and Whitehall in central London.

The landmark building was sold on 1 March 2016 by HM Government for more than £350 million, on a 250-year lease for conversion into a luxury hotel and residential apartments.

[2] The department of the Secretary at War was referred to as the 'Warr Office' (sic) from as early as 1694;[2] its foundation has traditionally been ascribed to William Blathwayt, who had accompanied King William III during the Nine Years' War and who, from his appointment as Secretary in 1684, had greatly expanded the remit of his office to cover general day-to-day administration of the Army.

In political terms, it was a fairly minor government job (despite retaining a continued right of access to the monarch) which dealt with the minutiae of administration, rather than grand strategy.

This powerful independent body, dating from the 15th century, had been directed by the Master-General of the Ordnance, usually a very senior military officer who (unlike the Secretary at War) was often a member of the Cabinet.

In practice, however, a large influence was retained by the conservative Commander-in-Chief Field Marshal Prince George, 2nd Duke of Cambridge, who held the post between 1856 and 1895.

His resistance to reform caused military efficiency to lag well behind that of Britain's rivals, a problem that became obvious during the Second Boer War.

Over the ensuing years it expanded into adjacent properties on Pall Mall before it was relocated to purpose-built accommodation, in what is now known as the Old War Office Building, in 1906.

[16] Between 1906 and its abolition in 1964 the War Office was based in a large neo-Baroque building designed by William Young, completed during 1906, and located on Horse Guards Avenue at its junction with Whitehall in Central London.

[17] On 1 June 2007 the building, other than the steps that give access to it, was designated as a protected site for the purposes of Section 128 of the Serious Organised Crime and Police Act 2005.

[19] In August 2013 it was announced that the building would be sold on the open market, with a goal of realising offers above 100 million pounds.

[21] The building's sale was completed on 1 March 2016 for more than 350 million pounds, on a 250-year lease, to the Hinduja Group (in partnership with OHL Developments) for conversion to a luxury hotel and residential apartments.