About the DC-4. Before it could be placed into service, the War Department took over all the production capacity for the duration of WWII. The military versions were the C-54 (Army) and R5D (Navy). The first DC-4's to go into scheduled airline service were actually conversions of the wartime production. Only 80 new DC-4's went into service after the war ended. A C-54 was specially converted to carry President Roosevelt, the first "Air Force One." The C-54 is depicted on the 32c Berlin Airlift stamp:

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