The Army Air Forces wanted a lengthened, pressurized version of the DC-4-based C-54 Skymaster transport with more powerful engines.

By the time the prototype XC-112A flew on 15 February 1946, the war was over, the USAAF had rescinded its requirement, and the aircraft was converted to YC-112A, being sold in 1955.

[1] A series of inflight fires (including the fatal crash of United Airlines Flight 608) grounded the DC-6 fleet in 1947.

The cause was found to be a fuel vent next to the cabin cooling turbine intake; all DC-6s were modified, and the fleet was flying again after four months on the ground.

The DC-6B, originally powered by Double Wasp engines with Hamilton Standard 43E60 constant-speed reversing propellers, was regarded as the ultimate piston-engine airliner from the standpoint of ruggedness, reliability, economical operation, and handling qualities.

[citation needed] The USAF and USN renewed their interest in the DC-6 during the Korean War and ordered 167 C-118/R6D aircraft, some of which later found their way to civil airlines.

[6] Many older DC-6s were replaced in airline passenger service from the mid-1950s by the Douglas DC-7, but the simpler, more economical engines in the DC-6 have meant the type has outlived the DC-7, particularly for cargo operations.

DC-6/7s surviving into the jet age were replaced in frontline intercontinental passenger service by the Boeing 707 and Douglas DC-8.

Many airlines and air forces from several countries included the DC-6 in their fleets at some point in time; these are further detailed in the list of Douglas DC-6 operators.