The United States' Supersonic Transport (SST) program was initiated by the Federal Aviation Administration (FAA) in 1963. The program aimed for a Mach 2+ aircraft capable of carrying approximately 300 passengers with intercontinental range. The US aimed to outstrip the British Aerospace/Aerospatiale Concorde and Soviet Tu-144 programs through the use of advanced technology and materials. By the late 1960s contracts had been let to prime contractors Boeing (airframe) and General Electric (engines) but the program was four to five years behind the European and Soviet efforts, which had graduated to supersonic flight testing while the US program had yet to pass beyond the mockup stage. In 1971 the slow pace of technical development, environmental concerns, high costs, and questions over the commercial feasibility of the aircraft led Congress to cancel the program.