Colt Model 608 CAR-15
The Model 608 was an attempt by Colt to provide an "Aviator Survival Carbine" for the USAF and was meant for use among downed aircrew.. The concept was to design a Carbine that could be disassembled into 2 parts and stored within the confines of aircraft cockpit. This carbine had many unique features to include: conical flashhider (or standard), no forward assist or a bayonet lug, round tubular handguards, cutoff pistol grip, and fixed tubular plastic-coated aluminum buttstock. With a 10-inch long barrel, the assembled weapon was 29 inches in overall length. The Model 608 never made into full scale production and there were very few actual models ever produced. Probably less than 10 exist today, the first picture below is from the ATF national refrence collection.
Photos and information from: Cesare