The Lockheed SR-71 Blackbird is one of the most iconic aircraft of the Cold War and a testament to Lockheed Skunk Works engineering of the era. The aircraft is one of the most famous black box projects built in secrecy, but it was also in many ways a bizarre design due to its requirements to solve extreme physical problems. Boom Supersonic says, “It purposely leaked fuel on the ground, had tires filled with nitrogen, and was made from one of the most expensive metals on earth. And, it’s still the world’s fastest plane.”