High Quality Content by WIKIPEDIA articles! The Douglas DC-4 is a piston-engined airliner and transport aircraft built by the Douglas Aircraft Company from 1942 to 1947. The type was originally designed as a commercial airliner, but until the end of World War II, all were built as military transports. After the war, many of these military aircraft were converted into commercial transports. Including military versions, more than 1200 DC-4s were built; a few are still flying today.