The C-135/KC-135 type was also known internally at Boeing as the Model 717, a name later assigned to a completely different aircraft.Įighteen C-135As (Boeing model number 717-157 ), powered by Pratt & Whitney J57 turbojets, were built. Forty-five base-model aircraft were built as C-135A or C-135B transports with the tanking equipment excluded three more aircraft originally ordered as KC-135A were factory converted to C-135A. The large majority of the 820 airframes of this type built were KC-135A Stratotankers, equipped to provide mid-air refueling to other aircraft. By the early 1970s, the C-135 fleet had been modified and relegated to other duties, which included staff/VIP transport, systems testing, and strategic reconnaissance. The Lockheed C-141 entered front-line service in April 1965, which finally gave MATS and its successor, Military Airlift Command, the strategic airlift capability it needed. Additionally, its takeoff and landing performance required long runways available only at the largest military bases or commercial airports, which were not necessarily located in close proximity to potential combat areas.
While range was greatly improved over earlier transports, it could not be augmented by aerial refueling, as C-135s were not configured with refueling receptacles. The aircraft's load floor was some 10 feet (3.0 m) off the ground, which required ground-handling equipment, its single side-loading cargo door was limited in what could fit through it, and its useful range was approximately 6,000 miles (9,700 km), insufficient to reach many of the Air Force's operating locations in Asia and the Pacific Rim. The C-135 was largely intended as an interim measure pending the development of more specialized jet transports such as the Lockheed C-141 Starlifter, and as such it incorporated numerous compromises in its strategic airlift capability. Ultimately, only 15 C-135As would be produced (in addition to three converted from KC-135s while still on the assembly line), with 30 additional aircraft being delivered as C-135Bs with the improved Pratt & Whitney TF33 turbofan engine. In May 1960, Congress approved the purchase of 50 C-135 aircraft it was selected in part because of its low development cost, being a straightforward derivative of the KC-135 tanker already in production. While capable of carrying large, outsized payloads, they were becoming increasingly obsolescent and lacked the global reach required of the rapidly-modernizing Air Force. In the early 1960s, the Military Air Transport Service operated a fleet consisting almost entirely of propeller-driven aircraft such as the piston-powered Douglas C-124 Globemaster II and C-133 Cargomaster turboprop.
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