With the rapid evolution of civil aviation in the mid-1930s and building on the success of the DC-3, five airlines - American, Eastern, Pan American, TWA, and United - each committed $100,000 to the Douglas Company for the development of a prototype of a large, long range transport.  In 1936 the specifications for the airplane were completed for the DC-4. The project was an ambitious one: provisions for 42 passengers, a range of 2,200 miles, power-boosted controls, an auxiliary power system, and air conditioning with provisions for a pressurized cabin in the production models.  The prototype made its maiden flight on June 7, 1938 from Clover Field, and  the next year was used for suitability trials by United Air Lines. Although the airplane had good flying qualities and was a big step forward in passenger comfort, the DC-4 was ahead of its time: The complicated systems caused unacceptable reliability. This, and the airplane’s high operating costs, led TWA and Pan American to lose interest and move to Boeing’s smaller 307 Stratoliner.  Eastern, American and United asked Douglas to simplify the design, leading the company to abandon the existing configuration (which was renamed DC-4E - for experimental), remove the complexity to better satisfy a realistic  airline environment, and start a new, simpler, more reliable DC-4 development.

Santa Monica engineering led by Arthur Raymond and E.F. Burton, redesigned the DC-4 to become a  25% lighter, less complicated airplane.  The tricycle landing gear arrangement with a steerable nosewheel was retained, but the power controls and air conditioning were dropped (the type was offered with an optional pressurized cabin, but no DC-4 were ever built with this feature.) The fuselage had a constant cross section fore and aft of the wing which made the development of stretched variants more practical.  The post war DC-6 and DC-7s benefitted from this design principle.

Before the new airliner made its maiden flight on Valentines Day 1942, the United States had entered WWII and the production of the aircraft was shifted to the US Army Air Corps and given the model number, C-54 and the name “Skymaster.”   The designation R5D was used for aircraft assigned to the Navy.

1,163 C-54/R5Ds were built for the United States military services between 1942 and January 1946.

Douglas continued to develop the type during the war in preparation for a return to airline services when peace returned, but after  VJ Day just 79 DC-4s were built before production ceased on August 9, 1947.  New planes had to compete in the market with some 500 C-54/R5Ds being offered as surplus by the US military.

C-54s and R5Ds gave the military the vital capability of long range cargo and passenger service to the far-flung theaters of operations in the global WWII. The aircraft had an outstanding record of safety and reliability: According to René Francillon, in his chapter on the  type, “during the war Skymasters completed 79,642 transocean flights with only three ditchings, of which one was a test.”

One aircraft, a VC-54 christened the "Sacred Cow", was the first airplane assigned to carry the president..  I was used to take President Roosevelt to the summit meeting in Yaltain April, 1945.

C-54s were operated by the Royal Air Force in the last year of the war, and the French were supplied with one aircraft as a gift from the USA for the use of General deGaulleafter VE Day.  When the airplane became widely available through surplus sales, at least fifteen other nations acquired the type for their armed services.

Many airlines acquired surplus planes and converted them for scheduled flights.  DC-4s opened the North Atlantic route to regular services by both US and European carriers.  Transpacific, South Atlantic, and Asian trunk services soon followed.  (All these blue ribbon routes became the first to be served by the DC-6, Constellation, and Stratocruiser pressurized, higher performance transports in just a couple of years after the DC-4 pioneered them.)

In June, 1948, Soviet occupation forces closed surface roads and rail access to Berlin in an attempt to deny any control of the partitioned city to the US, UK, and France.  The Allies immediately began to supply the city by air.  During the more than 13 months of its existence, the Berlin Airlift saw 278,228 flights deliver 2,326,406 tons of cargo, including 1.5 million tons of coal to a city of high importance to both east and west.  Skymasters formed the backbone of the fleet. At the peak of the operation 204 C-54s and 22 R5Ds were employed along the air corridors leading to Templehof from France and Belgium.  The historic airlift was so successful that the Soviets lifted the blockade in May 1949.