The Lockheed SR-71 "Blackbird" was an advanced, long-range, Mach

Mach number

Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...

 3+ strategic reconnaissance aircraft

Reconnaissance aircraft

A reconnaissance aircraft is a manned military aircraft designed, or adapted, to carry out aerial reconnaissance.-History:The majority of World War I aircraft were reconnaissance designs...

. It was developed as a black project

Black project

In the United States and United Kingdom, a black project is in the vernacular a classified military/defense project, unacknowledged publicly by the government, military personnel, and defense contractors. Examples of U.S...

 from the Lockheed A-12 reconnaissance aircraft in the 1960s by the Lockheed

Lockheed Corporation

The Lockheed Corporation was an American aerospace company. Lockheed was founded in 1912 and later merged with Martin Marietta to form Lockheed Martin in 1995.-Origins:...

 Skunk Works

Skunk works

Skunk Works is an official alias for Lockheed Martin’s Advanced Development Programs , formerly called Lockheed Advanced Development Projects. Skunk Works is responsible for a number of famous aircraft designs, including the U-2, the SR-71 Blackbird, the F-117 Nighthawk, and the F-22 Raptor...

. 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

Surface-to-air missile

A surface-to-air missile or ground-to-air missile is a missile designed to be launched from the ground to destroy aircraft or other missiles...

 launch was detected, the standard evasive action was simply to accelerate and outrun the missile.

The SR-71 served with the U.S.