In late 1945, several hundred C-54s were surplus to U.S. military requirements and these were converted for civil airline operation, many by Douglas Aircraft at its aircraft plants. The aircraft were sold to airlines around the world. By January 1946, Pan American Airways was operating their Skymasters on transatlantic scheduled services to Europe and beyond. Trans-Pacific schedules from San Francisco to Auckland began on 6 June 1946. After disposal by the U.S. Air Force and U.S. Navy, many C-54s were modified for use in civilian firefighting and air tanker roles. This included fitting tanks inside and under the fuselage and the fitting of dumping and spraying equipment also on the wing trailing edges. C-54s continued in this role until the late 1990s.