Upon returning to the runway, it was discovered that some of the A-12’s equipment was installed backwards.
On Apr. 26, 1962, the top secret A-12 “Oxcart” made its first flight at a non-existent airfield in Nevada. The aircraft, codenamed “Article 121”, began oscillating badly in the air and disappeared into a dust cloud which Clarence “Kelly” Johnson, the aircraft’s designer, described as “horrible to watch.” According to Strategic Air Command & Aerospace Museum Facebook Page, upon returning to the runway, it was discovered that some of the A-12’s equipment was installed backwards. The error was corrected and subsequent flights were performed without a hitch.
The top secret CIA aircraft, the replacement for the U-2, could fly at Mach 3 ( over 2,000 miles per hour) at an altitude greater than 80,000 feet.
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.

Although it was meant to be the replacement for the U-2 spy plane, both it and the SR-71 were decommissioned before the U-2 (that still flies today).
According to Lockheed, 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.
The following is a spec-sheet from the CIA’s official website.’

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.

Photo credit: Lockheed Martin, U.S. Air Force and CIA