By 1941 the old Air Corps had been transformed into the Army Air Forces, and it selected a modified version of the DC-3 -- the C-47 Skytrain -- to become its standard transport aircraft. A reinforced fuselage floor and the addition of a large cargo door were the only major modifications. Every branch of the U.S military and all the major allied powers flew it. The U.S. Navy version was the R4D. The British and the Australians designated it the Dakota (a clever acronym composed of the letters DACoTA for Douglas Aircraft Company Transport Aircraft). By the end of World War II, more than 10,000 had been built.