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June 1, 1939 - The Douglas DC-4 made its first passenger flight from Chicago to New York.

The new DC-4 was developed under the darkening clouds of WW2, and upon the USA's entry into war all DC-4s then on the production line were requisitioned for the US military. The result was that the first DC-4 flew for the first time on February 14 1942 in military markings (as the C-54 Skymaster). The DC-4 was found to admirably suit the USAAF's requirement for a long range cargo transport, and 1162 were built through the war years.
As was the case with the DC-3, the end of war meant that much of that number were surplus and sold to the world's airlines. Further to this Douglas built an additional 78 DC-4s to new orders. Over the years the survivors have been passed down to charter and freight airlines, and today small numbers survive in service as freighters.
Notable developments of the DC-4 include Aviation Trader's much modified Carvair freighter (described separately) while Canadair built a number with RollsRoyce Merlin engines and pressurised fuselages. The DC-4 also formed the basis for the larger DC-6 and DC-7 which are described separately (the DC-4 was the first airliner to introduce a circular section, constant diameter fuselage which made stretching the basic aircraft relatively simple).