Douglas started examining the possibility of a four-engined transport aircraft with double the capacity of its DST before the latter’s first flight. With the backing of American, Eastern, Pan American, Transcontinental & Western Air (TWA) and United, a prototype featuring triple fins and tricycle landing gear - a significant innovation on an aircraft of its size - was built under the designation DC-4. Although technically impressive, the sponsoring airlines were concerned about the complexity of the DC-4 and its operating economics, leading Pan American and TWA to withdraw their funding and turn to the Boeing Stratoliner. Shortly afterwards, in mid-1939, the remaining three airlines persuaded Douglas to shelve the design and start work on a something less complex. Although an entirely new design, Douglas stuck with the DC-4 designation (an added confusion being that the DC-5 had already made its first flight by this time) and production was set to get under way against orders for 61 aircraft when the Imperial Japanese Navy bombed Pearl Harbor. (In the meantime, the original DC-4, now re-designated DC-4E, had been sold in Japan where it was secretly dismantled and reverse-engineered by the Nakajima Aircraft Company as the G5N1 Shinzan bomber.) The United States Army Air Force, without any strategic transport capability, took over the entire DC-4 order book and went on to purchase the aircraft in considerable numbers. Post-war production of a Merlin-engined version of the DC-4 was undertaken in Canada, largely to fulfil domestic requirements.
A handful of flying survivors remain in the United States, with two being operated commercially. Numbers stored or derelict seem set to decline with ten aircraft located on airfields in Arizona and Wyoming expected to be broken up soon. Just one Canadian-built example survives.
First flight: DC-4E - 7 Jun 38 (c/n 1601, NX18100); DC-4 - 14 Feb 42 (c/n 3050, 41-20137); DC-4M - 15 Jul 46 (c/n 101, CF-TEN-X)
Production: 1,316, as follows:
Santa Monica, CA
Chicago-Douglas Field, IL
First delivery: DC-4 - 20 Mar 42, to USAAF (c/n 3060, 41-20138); DC-4M - 19 Nov 46, to Trans Canada Airlines (c/n 102, CF-TEK)
Last delivery: DC-4 - 9 Aug 47, to South African Airways (c/n 43157, ZS-BMH); DC-4M - 25 Aug 50, to RCAF (c/n 101, 17525)
Variants (all built at Santa Monica unless otherwise stated): DC-4E - prototype with seating for up to 52 passengers, powered by 4 Pratt & Whitney R-2180-S1A1-G radials;
DC-4/C-54 Skymaster - initial production version of re-designed aircraft with airline-style seating for 26 passengers, powered by 4 Pratt & Whitney R-2000-3s;
C-54A - military transport version powered by R-2000-7 engines, featuring strengthened floor, large cargo door, and capacity for 50 troops or 32,500 lbs of cargo (56 transferred to the US Navy as R5D-1, becoming C-54N in 1962);
C-54B - C-54A with increased fuel capacity (30 to the US Navy as R5D-2/C-54P);
C-54D - C-54B powered by R-2000-11s (86 became R5D-3/C-54Q);
C-54E - C-54D with capability to be converted to passenger configuration and with revised fuel tank arrangement (20 became R5D-4/C-54R);
C-54G - troop carrier version, powered by R-2000-9s (13 became R5D-5/C-54S);
C-54GM North Star - licence-built version of C-54G, powered by Rolls-Royce Merlin 620 or 622 pistons;
DC-4M-2 - pressurised, airliner version of C-54GM with seating for up to 62 passengers;
C-4 Argonaut - DC-4M-2 optimised for British Overseas Airways Corporation featuring Merlin 626 engines and other British equipment);
C-4-1 - C-4 with minor equipment changes;
C-5 - VIP version, powered by Pratt & Whitney R-2800-CA15 radial engines;
XC-114 - C-54G powered by Allison V-1710-131s;
XC-116 - XC-114 equipped with thermal de-icing;
DC-4-1009 - post-war unpressurised version with cargo door deleted and seating for up to 44 passengers.
Conversions included: 38 C-54 to C-54M for use in hauling coal during the Berlin Airlift; 34 C-54D to SC-54D Rescuemaster by Convair at Fort Worth, TX, for use in the search and rescue role (re-designated HC-54D in 1962); 30 C-54E to MC-54M in 1951 for use as medevac transports in the Korean War; and 86 R5D-2 and R5D-3 brought up to R5D-5 standard. In addition, large numbers were converted as 44-seat passenger airliners and given the designation C-54-DC for civil certification purposes.