The unique XC-99 was the prototype of a very heavy transport developed from the B-36 bomber in the late 1940s. It has the honour of being the largest piston-engined land-based transport aircraft ever built. Too big to be practical then, the XC-99 didn’t pass the prototype stage. The only example built gave good services in the USAF, but it rarely flew full.
In this photo, the XC-99 in it early configuration -single wheel main gear & no nose radar- demonstrates its huge capacities: 59 tons of cargo or 400 troops!!