Douglas decided to produce a four-engine transport about twice the size of the DC-3 and, in 1938, developed the single DC-4E to carry 42 passengers by day or 30 by night. It had complete sleeping accommodations, including a private bridal room.

It proved too expensive to maintain, so airlines agreed to suspend development in favor of the less complex DC-4, but it was not put into commercial service until 1946. Its military derivative was the C-54 "Skymaster" transport, ordered by the U.S. Army Air Forces in 1942.

Douglas built 1,241 of the DC-4s and its military counterparts, including the R5D for the Navy. During the war, C-54s flew a million miles a month over the rugged North Atlantic -- more than 20 round trips a day. A special VC-54C, nicknamed the "Sacred Cow" by the White House press corps, became the first presidential aircraft, ordered for Franklin D. Roosevelt.

In the years immediately following the war, new DC-4s and used C-54s carried more passengers than any other four-engine transport. Some were still flying through 1998.

After World War II, commercial airlines placed more than 300 civilian DC-4 transports into service