The Douglas Aircraft Company DC-4 is an American four-engine airliner. It first flew in February 1942; all production went to the US Military during World War II. Entered airline service post-war and proved to be popular and reliable.

Designated as the C-54 Skymaster with the USAAF and R5D with the US Navy, the type remained in military service into the 1960s. The North Star, a Canadian development based on the DC-4, designed in the 1940s, used Rolls-Royce Merlin engines. The Aviation Traders ATL-98 Carvair was a Douglas DC-4-based air ferry carrying 25 passengers and five cars loaded at the front. Production of the DC-4 ended in 1947 with 1245 airframes built.

Airframe construction is mainly of aluminium alloy, a semi-monocoque fuselage. The low mounted wings and the single fil tail assembly are of a cantilever design. The retractable undercarriage is a tricycle type. The flight crew typically consists of six; two pilots, a radio operator, navigator, and two relief crew; passenger cabin seats up to 86 passengers or 9,980 kg (22,002 lb) of cargo.

The DC-4 uses four Pratt & Whitney R-2000 Twin Wasp 14-cylinder air-cooled radial piston engines, mounted two per wing, driving three-bladed Hamilton-Standard Hydromatic, constant-speed propellers. It has a maximum speed of 450 km/h (280 mph), a cruise speed of 365 km/h  (227 mph), a service ceiling of 6,700 m (22,000 ft), and a range of 5,3oo km (3,300 mi).