The IMP was designed by Dale Davis of the USAF Armament Laboratory at Elgin, Florida. Its purpose was to provide a better survival rifle for aircrew personnel. Thus, it had to be very compact, whilst still offering more firepower than a standard pistol. Davis designed in the bullpup layout with a short barrel and no buttstock. Instead, the rear end of the weapon was designed to rest on the shooter's forearm, whether it be the left arm or the right. This was possible through a unique rotation system that allowed the rear end to swivel through three different angles, with three sets of sights to align with each configuration. Thus, it could rest along the firer's arm comfortably without the magazine getting in the way. Five prototypes were produced by Colt by 1972.
The IMP was chambered for the .221 Remington Fireball and could fire an experimental military version of it made specifically for the weapon, the .221-17 IMP, which has a composite construction of a steel base with a nylon body, along with a sub-caliber .17 inch projectile settled in a six-part sabot.