The DC-4 airplane, introduced by the U.S. Army as the C-54 Skymaster in 1942, was not put into commercial service until 1946. Douglas built 1,241 of the DC-4 planes and its military counterpart, the C-54 Skymaster. During the war, C-54 Skymasters flew a million miles a month over the rugged North Atlantic - more than 20 round trips a day. A special C-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-4 planes and used C-54 planes carried more passengers than any other four-engine transport.