These fascinating pictures show how engineers in 1960s California secretly developed the SR-71 Blackbird for the US Air Force – a plane which still holds the record for being the fastest ever aircraft.
The Lockheed SR-71 Blackbird is a long-range, strategic reconnaissance aircraft and these once classified photos reveal how Lockheed built three types of Blackbird - A, B and C in top secret conditions in Burbank, California.
The aircraft were built by American aerospace company Lockheed under a 'black project' - a highly classified military defence project unacknowledged by the government until its declassification.
Since July 28 1976 the SR-71 Blackbird has held the world record for the fastest air-breathing manned aircraft with a record speed of 2,193.2mph.
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