The SR-71 was a long-range Mach 3+ strategic reconnaissance aircraft operated by the U.S. Air Force from 1964 to 1998. Developed in the 1960s by Lockheed as a “black” project from the Lockheed A-12, with its Skunk Works division responsible for many innovative design concepts, it flew reconnaissance missions at high speeds and altitudes to outrun threats; when a surface-to-air missile launch was detected, the standard evasive action was simply to accelerate and outfly the missile. Designed with basic stealthy characteristics, it served as a precursor to future stealth aircraft. Thirty-two aircraft were built; 12 were lost in accidents, but none to enemy action. Known by nicknames including Blackbird and Habu, it has held the world record for the fastest air-breathing manned aircraft since 1976, a record previously held by the YF-12. This aircraft is the sixth prototype, serial number 61-7955. Assembly began on 13 May 1964, and number 955 first flew on 17 August 1965. It served throughout its career as the Palmdale test aircraft until being replaced by SR-71A number 61-7972 in 1985. Last flown on 24 January 1985, number 955 accumulated 1,993.7 hours of flight time.