The 2.75-inch folding fin aerial rocket (FFAR) was originally developed by the U.S. Navy in the late 1940s as a supplement and/or replacement for aircraft guns in both air-to-air and air-to-ground applications.
The original intent as a weapon to knock down enemy aircraft failed to pan out so the Navy concentrated on developing it as an air-to-ground weapon for close support of combat troops.
Later the U.S. Army and Marine Corps also adopted the 2.75-inch rocket as a primary weapon for their newly developing squadrons of armed helicopters.
Until electronic filters were developed, early models of this rocket could be inadvertently ignited by electromagnetic radiation from powerful military radios. They could also be inadvertently ignited by battery operated test equipment as was the case in one Vietnam helicopter unit when two techs were trying to find a short in one of the rocket pods. A tech using a voltage meter caused one of the rockets to fire blowing through the other tech, killing him, and imbedding itself in a nearby bunker. The warhead did not detonate.
The typical 2.75-inch rocket was 4 feet in length (fins folded), and weighed approximately 20 pounds (that included a 2.7 kg (6 lb.) HE warhead). Velocity was 2425 fps and a maximum range of 10, 425 meters. It was an unguided, air-launched vehicle that was not very accurate.