<p>Like its stablemate the C-47, the Douglas C-54 was derived from the prototype of a civil airliner, the DC-4E, which was built to a specification initially drawn up by United Air Lines. United was joined quickly by American Airlines, Eastern Airlines, Pan American Airways and TWA, all five carriers agreeing to share the cost with Douglas in return for early delivery positions.
</p>
<p>Powered by four of the newly developed 1,400-hp (1,044-kW) Pratt & Whitney R-2180 Twin Hornet 14-cylinder radial engines, the DC-4E flew for the first time on 7 June 1938, with Carl Cover in command. The design was innovative, incorporating such relatively untried features as cabin pressurization, power-boosted controls, a 115-volt AC electrical system and an auxiliary power unit. This very complexity, problems with the engines, and the growing realization that the aircraft was too large for its payload-carrying capacity led to increasing lack of interest on the part of the sponsoring airlines. Although certification was achieved on 5 May 1939 and United carried out some route-proving trials, Douglas terminated development and the DC-4E was later sold to Dai Nippon Koku Kabushiki Kaisha in Japan.
</p>
<p>Work started immediately on a redesigned DC-4 which, at 50,000 lb (22,680 kg) gross weight and with seats for 42 passengers, was slightly smaller than the prototype. The cabin pressurization system, power-boosted controls and auxiliary power unit were deleted and the engines were replaced by four Pratt & Whitney Twin Wasps. The landing gear was also modified, the mainwheels retracting forward into the engine nacelles rather than sideways into the wings. Orders for 61 production standard DC-4As were placed by American, Eastern, Pan American and United on 26 January 1940, but war in Europe and the apparent inevitability of increased United States' involvement led the Roosevelt administration to boost the US Army Air Corps' transport capability with orders which included nine C-54s and 62 C-54As. The nine C-54s were part of the initial batch of 24 civil DC-4As laid down at Santa Monica, and the remaining 15 were diverted to the USAAC order early in 1942. The first production C-54 made its maiden flight on 26 March 1942 and all 24 were in service with the Air Transport Command's Atlantic Wing by October. They were slightly modified for military service by the addition of four 464-US gal (1,756-liter) fuel tanks in the fuselage, to bring the total capacity to 3,700 US gal (14,006 liters), conferring a range of 2,500 miles (4,023 km) with a 9,600-lb (4,354-kg) payload that included 26 passengers.
</p>
<p>The C-54A, 77 of which were built in Santa Monica and 117 at a new factory at Orange Place, Chicago, appeared in January 1943, featuring 33 bucket seats for troops, a large cargo door, stronger floor, cargo boom hoist and slightly larger wing tanks. The last increased total fuel capacity to 3,734 US gal 14,134 liters) and gross weight rose to 68,000 lb (30,844 kg), allowing a payload of 9,000 lb (4,082 kg) to be carried for over 3,000 miles (4,828 km).
</p>
<p>A need to carry larger loads over shorter sectors led to the development of the C-54B, in which two of the fuselage tanks were deleted in favor of a 499-US gal (1,889-liter) integral tank in each outer wing panel. Gross weight rose again, to 73,000 lb (33,112 kg), and up to 49 troops or 36 casualty litters could be accommodated. C-54B production totalled 89 at Santa Monica and 100 at Chicago.
</p>
<p>A single VC-54C, with the C-54A's fuselage tanks and C-54B outer wing panels, with tanks to give it a range of 5,500 miles (8,850 km), was delivered in June 1944 for the use of President Roosevelt. In the same month, a C-54B was delivered to the Royal Air Force for the use of Winston Churchill, fitted out with a 10-seat VIP cabin by Armstrong Whitworth Aircraft and operated by No. 24 Squadron until November 1945, when it was returned to the United States.
</p>
<p>Replacement of the C-54B's Pratt & Whitney R-2000-7 engines by -11 models produced the C-54D, 304 of which were built for the USAAF at Chicago. Ten were supplied to the Royal Air Force under Lend-Lease, serving with No. 47 Group's Nos 232 and 246 Squadrons on routes to the Far East.
</p>
<p>Between January and June 1945, the Santa Monica plant manufactured 105 USAAF C-54Es, a long-range version with 3,600 US gal (13,627 liters) of fuel wholly contained in wing tanks. The final production version was the C-54G, with 1,450-hp (1,081-kW) R-2000-9 engines, which was developed for the India-China Wing's operations over the 'Hump', the 10,000-16,500-ft (3050-5,030-m) mountain ranges between the US bases on the plains of Assam and the Chinese air force bases, principally that at Kunming. USAAF procurement of C-54Gs totalled 162, all built at Santa Monica. In August 1945, USAAF Air Transport Command was operating 839 C-54s of all models on a worldwide route network.
</p>
<p>The US Navy, with a particular responsibility for air transport in the Pacific, acquired 183 aircraft from the USAAF production lines between 1943 and 1945. This total comprised 19 R5D-1s (C-54A), 11 R5D-2s (C-54B) and 20 R5D-4s (C-54E) built at Santa Monica; and 38 R5D-1s, 19 R5D-2s and 76 R5D-3s (C-54D) built at Chicago. The aircraft equipped squadrons of the Naval Air Transport Service until that formation was disbanded in July 1948, some units then becoming part of the combined Military Air Transport Service.
</p>
<p>The R5D-5 was a planned US Navy version of the C-54G, but none was delivered as such, although some R5D-2s and -3s were later converted to that standard, with R-2000-9 engines. Cargo aircraft converted to passenger configuration were given an -R suffix, as in the case of the R5D-4R and R5D-5R, and the -Z suffix denoted aircraft with much improved interior furnishing. Redesignation of the R5D fleet in 1962 resulted in the R5D-1, R5D-2, R5D-3, R5D-4R, R5D-5 and R5D-5R becoming the C-54N, C-54P, C-54Q, C-54R, C-54S and C-54T, respectively. Two single-example conversions for the US Coast Guard were the EC-54U, with special electronic equipment, and the RC-54V photographic surveillance variant.
</p>
<p>Postwar USAF versions included an experimental XC-54K with 1,425-hp (1,063-kW) Wright R-1820-HD engines, a C-54L with a modified fuel system, 38 C-54Ms stripped to increase payload by 2,500 lb (1,135 kg) for coal-carrying operations during the Berlin Airlift, and 30 C-54Es converted in 1951 as MC-54M ambulance aircraft for the evacuation of wounded personnel from Korea. Other specialized-role conversions included 38 SC-54Ds modified for the USAF Air Rescue Service in 1955, nine JC-54 range support aircraft used for missile nosecone recovery, and a small number of AC-54Ds for navaid calibration.
</p>
<hi style=hdr1>Specification</hi>
<list style=aflst>
<item><hi format=bold>Type:</hi> cargo and passenger transport
<item><hi format=bold>Performance:</hi> maximum speed 274 mph (441 km/h) at 14,000 ft (4,265 m); cruising speed 239 mph (385 km/h) at 15,200 ft (4,635 m); service ceiling 22,000 ft (6,705 m); range 3,900 miles (6,276 km)
<item><hi format=bold>Weights:</hi> empty 38,000 lb (17,237 kg); maximum take-off 73,000 lb (33,112 kg)
<item><hi format=bold>Dimensions:</hi> span 117 ft 6 in (35.81 m); length 93 ft 11 in (28.63 m); height 27 ft 6 in (8.39 m); wing area 1,463 sq ft (135.91 m<su>2</su>)
