On 3 May 1943, while on an aerial inspection tour, Lieutenant General Frank M. Andrews, European Theater of Operations, United States Army (ETOUSA) commander since replacing Eisenhower on 5 February 1943, was killed in an aircraft crash in Iceland. Marshall appointed Devers to take command of ETOUSA in his place. Devers arrived in England on 9 May 1943. His principal tasks were overseeing preparation of detailed plans and the buildup of men and materiel for Operation Overlord, and supporting the Combined Bomber Offensive. At the end of May 1943, there were 133,000 US troops in the United Kingdom, of which 19,000 were in the ground forces, 74,000 in the air forces, and 34,000 in the services of supply. By the end of the year, their numbers had grown to 774,000, of which 265,000 were in the ground forces, 286,000 in the air forces, and 220,000 in the services of supply. In preparing the plans for Overlord, he worked closely with the Chief Of Staff to the Supreme Allied Commander (COSSAC), British Lieutenant General Frederick E. Morgan, with whom he had a good working relationship. Devers' main objection to the COSSAC plan was that he did not want American units smaller than corps directly subordinated to British command, based on what he called "the Pershing Principle".