OSS/London

OSS/London, originally known as COI/London or the London Outpost, was the largest foreign headquarters complex of the Office of Strategic Services (OSS) during World War II, operating out of several buildings in the area near Grosvenor Square, Mayfair, London, which maintained the command and control over all OSS servicemembers stationed in the United Kingdom and agents deployed to Western Europe, and for the bulk of the war, operated as the headquarters of OSS/Europe. From OSS/London, operations were planned alongside the British Secret Intelligence Service (MI6) and the Special Operations Executive (SOE) to deploy officers and agents throughout Europe for missions of sabotage, clandestine operations, covert operations, espionage, and other mission sets.

OSS/London began with a single staffer from the Office of the Coordinator of Information (COI) assigned as a Liaison officer to the British government working down the road at the Macdonald House. The first three specific offices for OSS/London were located at 59, 71, and 72 Grosvenor Street, but by the end of the war it had expanded to Mount Row, Brook Street, Portman Square, and Mount Street. The facilities management and procurement were undertaken by OSS/London's transportation section. For some time, the X2 Counterintelligence Section was based out of 7 Ryder Street (which has become 14 Ryder Street). At its peak staffing in 1944, there were 2,800 OSS personnel working under the command structure of OSS/London.