Douglas C-54 Skymaster (1942-1946): America's entry into World War II resulted in the U.S. Army taking over commercial DC-4 production before the first airliner could be completed. The plane made its first flight in February 1942 under the army designation C-54 Skymaster. Modifications to the original design included extra fuel tanks, a reinforced fuselage floor and the addition of side-by-side cargo doors. The C-54 could accommodate 50 troops with combat equipment, or carry 15,000 pounds of cargo on pallets, or airlift 30 patients on stretchers. The C-54 was known in the Navy as the R5D. Between 1942 and 1945, C-54s flew more than 20 round trips a day over the rugged North Atlantic. A single C-54C, nicknamed Sacred Cow, was built as the first official presidential aircraft. When the last C-54 was delivered in January 1946, Douglas had built 1,165 Skymasters. After the war C-54s gained fame as the principle transport used during the 1948-1949 Berlin Airlift.