Archibald Sinclair, 1st Viscount Thurso (22 October 1890 – 15 June 1970) was a Scottish politician and leader of the Liberal Party. After an education at the Royal Military College, Sandhurst, Sinclair served on the Western Front during the First World War, rising to the rank of Major and working under J. E. B. Seely and Winston Churchill. After the war he worked with Churchill again when the latter was Secretary of State for War and Secretary of State for the Colonies. Sinclair entered the House of Commons as a Liberal MP in 1922, rising to become the party's Chief Whip by 1930. When the Liberal Party joined the National Government of Ramsay MacDonald in 1931, Sinclair was appointed Secretary of State for Scotland, holding the post until his party resigned from the government in 1932. He took over as Liberal Party leader in 1935 after incumbent Herbert Samuel lost his seat in the election. Sinclair returned to government as Secretary of State for Air in 1940, under Churchill's all-party Second World War coalition government. In this role he worked with the Royal Air Force (RAF) to plan the Battle of Britain. Sinclair remained a minister until the end of the coalition in 1945, but then lost his seat in the 1945 general election. He was elevated to the House of Lords in 1952. This portrait of Sinclair was taken by the RAF official photographer during the Second World War.Photograph credit: Royal Air Force official photographer