An interesting aspect of the XC-99 program was Convair's almost successful attempt at turning the massive double-decker cargo-ship into a luxury airliner.

An XC-99 airplane occupies a berth at Kelly AFB in this photo taken June 19, 1952. Based at Kelly during the 1950s, the huge, experimental cargo plane ferried parts and supplies among air bases.

As peacetime began, Douglas and Lockheed were developing large piston-powered military transports, the Globemaster and Constitution, while Convair had set the bar even higher with its XC-99 ...

Even as Convair was developing the B-36, it began work on the Convair Model 37, a planned civil passenger jet based on the bomber. ... The sole prototype, designated the XC-99, ...