The Lockheed SR-71 "Blackbird" was an advanced, long range, Mach 3+ strategic reconnaissance aircraft. It was developed from the Lockheed A-12 reconnaissance aircraft in the 1960s by the Lockheed Skunk Works as a black project. Clarence "Kelly" Johnson was responsible for many of the design's innovative concepts. During reconnaissance missions the SR-71 operated at high speeds and altitudes to allow it to outrace threats; if a surface-to-air missile launch was detected, standard evasive action was simply to accelerate. The SR-71 was in service with the U.S. Air Force from 1964 to 1998. Twelve of the 32 aircraft were destroyed in accidents; none were lost to enemy action. The SR-71 was unofficially named the Blackbird, and called the Habu by its crews, referring to an Okinawan species of pit viper. Since 1976, it has held the world record for the fastest air-breathing manned aircraft, a record previously held by the YF-12.