Even before the first operational flight of the legendary Lockheed U-2 spy plane, aircraft design genius Kelly Johnson began work with his team at the company's "Skunk Works" plant on the type's replacement. The result was the SR-71. First deployed on March 9, 1968, this tri-sonic 'hotrod' flew its first operational sortie over North Vietnam just 12 days later. On that debut mission, the Blackbird overflew surface-to-air missile sites with complete impunity, collecting the detailed intelligence that led directly to the end of the siege of Khe Sanh in the process.