In the mid-1950s, NATO officials became concerned with the possibility that Soviet nuclear weapons could obliterate Allied aircraft sitting on the ground at their airfields in a surprise attack, leaving NATO powerless to retaliate. One of the potential cures for this problem was to disperse aircraft in hardened shelters far away from targeted airfields, and having these aircraft launched by rocket propulsion from special platforms. The concept was known as Zero-Length Launch, or ZEL for short.
A contract change made on October 12, 1956 stipulated that NAA would build the last 148 F-100D aircraft with ZEL capability. Two F-100Ds (56-2904 and 56-2947) were loaned by the USAF to NAA for tests of the ZEL system.
In order to launch the F-100D, NAA's Rocketdyne division developed a solid-fuel rocket motor that would be attached to the bottom of the rear fuselage. This engine was capable of delivering a thrust of 130,000 pounds for four seconds. This was sufficient to accelerate the F-100D from zero to 300 mph in four seconds. Following burnout, the rocket motor would drop off the aircraft, leaving the Super Sabre free to fly.
The first five launches took place with dummy airplane-shaped masses attached to the rocket motor. The first such launch took place on December 12, 1957.
The first live launch of an F-100D took place on March 26, 1958. On that day, test pilot Al Blackburn climbed into 56-2904, started the engine, pushed the throttle to full afterburner, then lit the rocket motor. Within four seconds, he was flying at 300 mph. The rocket booster dropped off, and Blackburn entered the standard pattern and landed safely.
On his second flight, things did not go so well. After burnout, the rocket motor would not drop off the aircraft and Blackburn was forced to eject. However, the remaining of the total of 20 launches were incident-free. Airplanes taking place in test launches carried standard underwing stores, including dummy nuclear weapons.
Although the system was reliable and relatively simple to operate, it was never deployed operationally.