Known as ''Blackbird'', the SR-71 was a US Air Force (USAF) long-range strategic reconnaissance aircraft that served between 1964 and 1998. Operating at high altitude (24,000m) and cruising at speeds of Mach 3.2, it could simply outrun surface-to-air missiles. The SR-71 was developed as a black project by the Lockheed Skunk Works. A total of 32 aircraft were built, and as testament to its effectiveness, none were ever lost in combat despite being fired on 4,000 times. However, twelve Blackbirds were lost to accidents. Much of the airframe is made of titanium in order to address the issue of high temperatures created by supersonic speeds. The panels were designed for thermal expansion, meaning on the ground they only fitted loosely, before reaching proper alignment in flight. The SR-71 holds the record for the fastest air-breathing manned aircraft when it attained a speed of 3529km/h, propelled by its Pratt and Whitney J58-P4 engines. The SR-71 was used extensively in combat in the skies over Vietnam and Laos, and throughout the course of its career this revolutionary aircraft completed 17,300 sorties.