Douglas DC - 6 The Douglas DC - 6 is a piston - powered airliner and transport aircraft built by the Douglas Aircraft Company from 1946 to 1958 . Originally intended as a military transport near the end of World War II , it was reworked after the war to compete with the Lockheed Constellation in the long - range commercial transport market . More than 700 were built and many still fly today in cargo , military and wildfire control roles . The DC - 6 was known as the C - 118 Liftmaster in United States Air Force service and as the R6D in United States Navy service prior to 1962 , after which all U . S . Navy variants were also designated as the C - 118 . Design and development . The United States Army Air Forces commissioned the DC - 6 project as the XC - 112 in 1944 . The Army Air Forces wanted a lengthened pressurized version of the popular 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 By the time the prototype XC - 112A flew on 15 February 1946 the war was over , the USAAF had rescinded its production requirement for the transport , and the aircraft was converted to " YC - 112A " , being sold in 1955 . Douglas Aircraft modified the design into a civil transport and the civil DC - 6 first flew on 29 June 1946 , being retained by Douglas for testing . The first airline deliveries were made to American Airlines and United Airlines on 24 November 1946 . 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 . Operational history . In April 1949 United , American , Delta , National and Braniff were flying DC - 6s in the United States . United flew them to Hawaii , Braniff flew them to Rio de Janeiro , and Panagra flew Miami - Buenos Aires ; KLM , SAS and Sabena flew DC - 6s across the Atlantic . BCPA DC - 6s flew Sydney to Vancouver and Philippine flew Manila to London and Manila to San Francisco . Pan Am used DC - 6Bs to start trans - Atlantic tourist class flights in 1952 . These were the first DC - 6Bs that could gross 107 , 000 lb , with CB - 17 engines rated at 2 , 500 hp on 108 / 135 octane fuel . Several European airlines followed with their own transatlantic services . The DC - 6A / B / C sub - types could perhaps fly non - stop from the eastern US to Europe but needed to refuel in Newfoundland ( and perhaps elsewhere ) when westbound against the wind . Douglas designed four variants of the DC - 6 : the basic DC - 6 , and the longer fuselage , higher - gross - weight , longer - range versions — the DC - 6A with cargo doors forward and aft of the wing on the port ( left hand side ) with a cargo floor ; the DC - 6B for passenger work , with passenger doors only and a lighter floor ; and the DC - 6C convertible , with the two cargo doors and removable passenger seats . 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 . The military version , similar to the DC - 6A , was the USAF C - 118 Liftmaster ; the USN R6D version used the more powerful R - 2800 - CB - 17 engines . These were later used on the commercial DC - 6B to allow international flights . The R6D Navy version ( in the late 1950s and early 1960s ) had Curtiss Electric constant - speed reversing propellers . 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 . Harry Truman ' s first presidential aircraft was an Air Force short fuselage DC - 6 which was designated VC - 118 , and named " The Independence " . It is preserved in the National Museum of the United States Air Force at Dayton , Ohio Total production of the DC - 6 series was 704 , including military versions . In the 1960s two DC - 6s were used as transmitter platforms for educational television , based at Purdue University , in a program called MPATI ( Midwest Program on Airborne Television Instruction ) . 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 has meant that the type has outlived the DC - 7 , particularly for cargo operations . DC - 6 / 7s surviving into the Jet Age were replaced in front line inter - continental passenger service by Boeing 707 and Douglas DC - 8 aircraft . 2006 marked the 60th anniversary of the introduction of the DC - 6 . Basic prices of a new DC - 6 in 1946 – 47 was around £210 , 000 – £230 , 000 and had risen to £310 , 000 by 1951 . By 1960 used prices were around £175 , 000 per aircraft . Prices for the DC - 6A in 1957 – 58 were £460 , 000 – £480 , 000 . By 1960 , used prices were around £296 , 000 . Equivalent prices for the DC - 6B in 1958 were around £500 , 000 . Used prices in 1960 were around £227 , 000 . Operators . Current operators . Today most DC - 6s are inactive , stored , or preserved in museums ; although a number are still flying in northern bush operations in Alaska and Canada , while several are based in Europe and a few other DC - 6s are still in operation for small carriers in South America . Former operators . A great number of 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 article listing the operators of the Douglas DC - 6 . Survivors . Several DC - 6s are preserved in museums . In all , There are 147 surviving aircraft including 47 airworthy ones . Specifications . A note of interest is that the diagram depicts the sleeper version of the early short fuselage DC - 6 . The very small windows above the standard ones permitted passengers in their Pullman - style bunks a view of the outside .