Boeing C-135 Stratolifter

The Boeing C-135 Stratolifter is a transport aircraft developed from the Boeing KC-135 Stratotanker and the basis of a number of variants performing different roles; the first was built in August 1956 and the C-135 and its variants have been a fixture of the United States Air Force ever since. In the early 1960s the Military Air Transport Service flew almost entirely propeller-driven aircraft such as the Douglas C-124 Globemaster II and the turboprop C-133 Cargomaster, which were becoming obsolescent, and in May 1960 Congress approved the purchase of 50 C-135s, chosen partly for the low development cost of a straightforward KC-135 derivative. Only 15 C-135As were produced, plus three converted on the assembly line, and 30 more were delivered as C-135Bs with Pratt & Whitney TF33 turbofans. It was an interim measure, with a load floor about 10 feet off the ground, a single side cargo door and no aerial refuelling receptacle.