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. Other changes included the fitting of cargo hooks beneath the center wing section and the removal of the tail cone to mount a hook for towing gliders.