The Lockheed SR-71A Blackbird flew classified reconnaissance missions at Mach 3+ near sensitive and potentially hostile areas all over the world. The aircraft only had enough fuel for just over one hour at operating altitude, so it was only thanks to air-to-air refuelling tanker aircraft that the SR-71 could traverse the globe on long missions. Consequently, the Blackbird had its own dedicated fleet of Boeing KC-135 Stratotankers. These ‘Q’ models carried the SR-71’s special JP-7 fuel. Latterly, some McDonnell Douglas KC-10 Extenders were also used, but the majority of the task fell to the KC-135Qs.