The Douglas C-47 is arguably the most successful aircraft to come out of World War II. It was designed in 1935 as the DC-3 commercial airliner. The aircraft was so far ahead of its competitors that over 400 had been built by 1940 when the U.S. Army Air Forces expressed an interest in a militarized cargo and troop transport version. The main modifications from the DC-3 version are a large cargo door on the left side of the aircraft and a strengthened floor. More than 9,500 Skytrains were built for all branches of the American military and for export. Large numbers of C-47s entered civil service after the war and as many as 400 of them were still flying around the world in 2017.
U.S. Army Air Forces, England, June 6, 1944
Pima Air & Space Museum