What was the L-949 "Speedfreighter"?

The L-949 Speedfreighter only makes sense in light of the model it was based on. The L-749 was the longer-range version of the short-fuselage Constellation, and its evolution, the L-749A, on sale from the summer of 1948, is considered the pinnacle of that series: 60 were built. Lockheed planned a further step, the L-849, which would have been an L-749 with Wright R-3350 TurboCompound engines. Building on that L-849, it in turn proposed the L-949 Speedfreighter: a combined cargo-and-passenger version with the fuselage stretched by 18 ft 4 in.

The idea addressed a known limitation. On the L-749 and L-749A, the cargo holds weren't large enough to make full use of the available payload, so Lockheed designed an external container, the Speedpack, which was attached under the center of the fuselage with quick-release fittings, held 2,000 kg, and was fitted only when needed. A longer fuselage with room for both freight and passengers was the underlying solution to that same problem.

The Speedfreighter never got past the drawing board, but its two key ingredients ended up materializing in another aircraft. Lockheed stretched the XC-69 prototype by 18 ft (5.5 m) to turn it into the basis for the L-1049 Super Constellation, which flew in 1950. The R-3350 Turbo-Compound engines were approved for civilian use in 1953, and Lockheed fitted them to the L-1049C, whose first flight took place on February 17 of that year. So the stretch and the engines that the L-949 combined in a mixed freighter did eventually reach the airlines, through the Super Constellation family, which also had cargo versions.