The Mk 18 Mod 0 is an American military carbine based on the M4A1. The Mk 18 Mod 0 consists of an M4A1 carbine equipped with the Close Quarter Battle Receiver (CQBR) upper receiver.
It features a 10.3-inch Colt barrel, Daniel Defense RIS handrail, and is usually fitted with an optic and back-up iron sights.