In 1963, three ex-USAF F-104As (56-756, -760, and -762) were taken out of storage at Davis Monthan AFB and modified as NF-104A aerospace training aircraft. All of the military equipment was removed and the original F-104A vertical fin was replaced by the larger fin that was used on the F-104G. The wingspan was increased by four feet (to 25.94 feet) and a set of hydrogen peroxide control thrusters were mounted at the nose, tail, and wingtips. A 6000 pound thrust Rocketdyne LR121/AR-2-NA-1 auxiliary rocket engine was mounted on the tail above the jet exhaust pipe. This rocket engine could be throttled from 3000 to 6000 pounds of thrust, and the burn time was about 105 seconds.
The first NF-104A was delivered on October 1, 1963, with the other two following a month later. They were operated by the Aerospace Research Pilot School at Edwards AFB, which was commanded at that time by Colonel Charles E. "Chuck" Yeager.
On December 6, 1963, the first NF-104A set an unofficial world altitude record of 118,860 feet for aircraft taking off under their own power. The official record at that time was 113,829 feet, set by the Mikoyan/Gurevich Ye-66A, an experimental version of the MiG-21 Fishbed. Later, the same NF-104A flown by Major R. W. Smith reached an altitude of 120,800 feet.
On December 10, 1963, the second NF-104A (56-762), with Chuck Yeager at the controls, went out of control at an altitude of 104,000 feet and fell in a flat spin to 11,000 feet. Yeager managed to eject successfully at that altitude, although he was badly burned on his face by the rocket motor of his ejector seat. The aircraft was destroyed in the ensuing crash. An investigation later showed that the cause of the crash was a spin that resulted from excessive angle of attack and lack of aircraft response. The excessive angle of attack was not caused by pilot input but by a gyroscopic condition set up by the J79 engine spooling after shut down for the rocket-powered zoom climb phase. So it wasn't Chuck's fault.
In June of 1971, the third NF-104A, with Capt. Howard C. Thompson at the controls, suffered an inflight explosion of its rocket motor. Although Thompson was able to land safely, the aircraft's rocket motor and half its rudder were blown away. Since the program was about to end in any case, this aircraft was retired.
The number one NF-104A is currently on display on top of aa pylon in front of the USAF Test Pilot School.