Slessor played a key role in planning the force structure and strategic concept for the RAF in World War II while serving as director of plans for the Air Staff from 1937 to 1941. He was an advocate for a heavy bomber force and for offensive strategic bombing operations. Slessor was often involved in coordination and planning with senior American leaders throughout the war, including the January 1943 Casablanca Conference and the "ABC" staff discussions among the Americans, British, and Canadians to coordinate Allied plans should the United States enter the war.
Slessor held a series of important command and staff positions throughout the war. In May 1941, he assumed command of 5 Bomber Group. In February 1942, he returned to the Air Staff and a newly created position, assistant chief of the Air Staff (Policy). In February 1943, he was appointed air officer commander in chief of Coastal Command. In this post, he directed the successful offensive of land-based aircraft against German submarines transiting the Bay of Biscay. In May 1944, Slessor became commander of the RAF Mediterranean and Middle East forces. In this position, he was also deputy commander of the Mediterranean Allied Air Forces under U.S. Army Air Forces Major General Ira Eaker. Slessor also helped plan and direct the air components of the final phase of the Italian Campaign and the Allied landing in southern France, Operation dragoon.
In April 1945, Air Marshal Slessor returned to the Air Ministry as the air member for personnel, with responsibility for planning the demobilization of the wartime force and the development of the peacetime force structure of the RAF. Sir John Slessor ended his military career as marshal of the RAF and chief of the Air Staff from 1950 to 1952. He subsequently published two books on defense policy and an autobiography. He died in Wroughton, England, on 12 July 1979.
Jerome V. Martin
Franks, Norman L. R. Conflict over the Bay. London: William Kimber, 1986.; Probert, Henry. High Commanders of the Royal Air Force. London: Her Majesty's Stationery Office, 1991.; Slessor, Sir John Cotesworth. Central Blue: The Autobiography of Sir John Slessor, Marshal of the RAF. New York: Praeger, 1957.; Terraine, John. The Right of the Line: The Royal Air Force in the European War, 1939–1945. Ware, Hertfordshire, UK: Wordsworth Editions Limited, 1997.