Gas turbine engines are often categorised into turbojets, turbofans, turboprops and turboshafts. The most common reaction propulsion engines flown are turbojets, turbofans and rockets. Turbofans were invented to circumvent the undesirable characteristic of turbojets being inefficient for subsonic flight. Other successes followed, including the T58, and T64 turboshaft engines, J85 and F404 turbojets. Rolls-Royce Avon turbojets replacing the pair of turboprops. Compressor types used in turbojets were typically axial or centrifugal. Its powerplant comprised two RD-20 turbojets, which were Soviet-manufactured versions of the BMW 003. The T-2C was fitted with two thrust General Electric J85-GE-4 turbojets. The last major aircraft to use turbojets were Concorde and Tu-144 supersonic transports. It was powered by a pair of de Havilland Gyron Junior turbojets, producing of thrust. Fifteen C-135As, powered by Pratt & Whitney J57 turbojets, were built. Pratt & Whitney JT3C-6 turbojets with water injection. Westinghouse XJ34-WE-13 turbojets, flew from Muroc on 20 October 1948. The XF-89 was fitted with Allison J35-A-9 turbojets and proved to be seriously underpowered. This aircraft, powered by two Mikulin AM-5 turbojets first flew on 7 April 1959.