18 April 1958: At Edwards Air Force Base, California, test pilot Lieutenant Commander George Clinton Watkins, United States Navy, set a Fédération Aéronautique Internationale (FAI) World Altitude Record of 23,449 meters (76,932 feet) ¹ with a Grumman F11F-1F Tiger, Bureau of Aeronautics serial number (Bu. No.) 138647.
The F11F-1F had also reached an impressive Mach 2.04 in 1957, thus becoming the first naval aircraft in the world to exceed Mach 2 (two years before the F4H, the F8U-3 and the A3J).
The F11F-1F Tiger was a higher performance variant of the U.S. Navy F11F single-seat, single-engine swept-wing aircraft carrier-based supersonic fighter. As an improvement, Grumman proposed a more advanced version of the airframe known as the F11F-1F Super Tiger. This was the result of a 1955 study to fit the new General Electric J79 engine into the F11F airframe. The Navy was sufficiently interested to authorize modification of two production F11F-1s with enlarged air intakes and YJ79-GE-3 turbojets, with the result being designated the F11F-1F, indicating a production F11F-1 with a special engine fit.
The U.S. Navy determined that the F11F-2 was too heavy for operation aboard carriers and did not place any orders. The designation was changed from F11F-2 to F11F-1F, and later, to F-11B, although the remaining aircraft was no longer flying by that time.
The single remaining F11F-1F, Bu. No. 138647, is on static display at the Naval Air Weapons Center, China Lake, California.
Sources: This Day in Aviation History, c. Brian R. Swopes https://www.thisdayinaviation.com/18-april-1958/; Wikipedia.