In 1914 the Hillingdon House property was put on the market by the estate of Frederick Cox. It was described as "a brick and stone building, partly stuccoed, with extensive outbuildings and ornamental gardens." The house and gardens, together with the surrounding parkland and an artificial lake created by damming a section of the River Pinn, amounted to over 200 acres.The British Government purchased the estate in 1915, with the intention of establishing a prisoner of war camp. However, the local population strongly opposed the plan and the government relented. The site instead became the Canadian Convalescent Hospital to care for troops evacuated from the front line during the First World War. The hospital was opened on September 20, 1915 with the first patient being taken in on October 4, 1915. By October 17, 1916 the hospital reached a total number of 512 patients.
From the war diary of the Canadian Convalescent Hospital, Uxbridge (Volume 1, Oct 4, 1916)This hospital is located in College Park, Hillingdon, in the Parish of Hillingdon. The Main building is an old mansion and formerly belonging to the late Col. Cox, a late partner in the well-known banking institution of that name. The grounds consisting of about 40 or 50 acres are beautifully laid out with shrubbery and ornamental trees. They have a Southern exposure and are protected on the north and east by high ground at the bottom of the hospital grounds, runs a small stream. The walks and drives of the immediate vicinity of this hospital are very picturesque and beautiful, and in old times this locality was regarded by Londoners as a health resort. In addition to the Main building which is capable of holding about 115 patients, 16 Salonika huts have been erected during the season and this will bring the capacity of the hospital up to 500 beds. The Canadian Red Cross Society has erected a recreation building and a dining room, the latter capable of seating 200 people at once.
From Statistical Reports of admissions and discharges of the hospital:War Diary (Volume 1, Oct 4, 1916) October 1915 to September 1916.Admissions 2402Discharges 2308
The hospital was officially closed 12 December 12, 1917. The last patients and medical staff were transferred to other Canadian Hospitals in England on December 11, 1917.In November 1917 the Royal Flying Corps Armament School moved into Hillingdon House with 114 officers and 1156 men. Making a donation to the Canadian Red Cross, the RFC used parts of the estate not required by the Canadians and established firing ranges for the training of recruits in ground gunnery. (photos from a post card collection on loan to Wartime Heritage)