The      XC-99 was an American heavy transport aircraft derived from the B-36      strategic bomber. Its first flight took place in 1947, and its Air Force      service lasted from 1950 to 1957. The plane was the largest transport      aircraft of its time and could carry 400 fully equipped soldiers or 45      tons of cargo. The XC-99 set several world records in its time, and it      was also extensively used by the US Air Force during the Korean War.      There was a project to build a transcontinental passenger plane on its      basis, but this was canceled. The US Air Force did not issue further      orders for the type, and the XC-99 remained a single prototype. Until the      appearance of the C-5 Galaxy, it was the largest in its class.