The Lockheed SR-71, unofficially known as the Blackbird and by its crews as the Habu or the sled, was an advanced, long-range, Mach 3 strategic reconnaissance aircraft developed from the Lockheed YF-12A and A-12 aircraft by the Lockheed Skunk Works. The SR-71 line was in service from 1964 to 1998. Clarence "Kelly" Johnson was the man behind many of the design's advanced concepts. The SR-71 was one of the first aircraft to be shaped to reduce radar cross section. However, the aircraft was not stealthy and still had a fairly large radar cross-section. The aircraft flew so fast and so high that if the pilot detected a surface-to-air missile launch, the standard evasive action was simply to accelerate. Thirteen aircraft are known to have been lost, all through non-combat causes.