The A-12 Oxcart was a super-secret, single-seater spy plane and was more secret and much rarer than the SR-71. In fact, the SR-71 was actually developed from the A-12.
The iconic SR-71 Blackbird spy plane is known for being the official record holder for the fastest jet-powered, piloted aircraft of all time.

However, there has actually been a legitimate, jet-powered, piloted aircraft that was faster than the SR-71, the A-12 Oxcart.
‘The A-12 Oxcart was a super-secret, single-seater spy plane and was more secret and much rarer than the SR-71,’ says Christian Nelson, an aviation expert, on Quora. ‘In fact, the SR-71 was actually developed from the A-12.’

‘Despite bearing the marks of the USAF, it was developed for and only ever flown by the CIA. It was meant to be the replacement for the U-2 spy plane, though both it and the SR-71 was decommissioned before the U-2. I mean the U-2 still flies to this day, more than half a century after its first flight. So, fail marks on that account for the Ox-Bird sisters.

‘Anyway, according to Lockheed (who designed and built them) the A-12 Oxcart was officially able to fly at 95,000ft and at 2,221 mph or at Mach 3.35. Compare that to 85,000ft and 2,112mph or Mach 3.2 of the SR-71. Though there are anecdotal stories of both aircraft surpassing the official records for speed and altitude.
‘The CIA operated the A-12 slightly under its capacity it seems because their documented numbers are slightly lower than Lockheed’s; about 3mph slower and 5000ft lower.
‘Here’s a spec-sheet from the CIA’s official website.’

Nelson concludes:
‘Both planes can be viewed side-by-side in Blackbird Park situated within Air Force Plant 42 next to Palmdale Regional Airport in Palmdale, California. So, like, go see it or something.’

Photo credit: U.S. Air Force and CIA