The standard-issue rifle for U.S. Servicemen in Vietnam. Designed by Eugene Stoner as the Ar-15 to replace the M14 (which was difficult to control while in full-auto). The rifle fired .223 caliber ammunition, which later became the 5.56 mm NATO round in widespread use today. The M16A1 "spawned" the current U.S. service rifle, the M16A2, as well as the A3 (full-auto A2), and the M4 Carbine, which is in use by Special Forces units around the world.
The M16A1's jamming problems had nothing to do with the design of the gun, the U.S. Government had told troops that the rifle was self cleaning, therefore the troops were not issued cleaning kits until 1968. After the kits were issued, jamming reports were nearly unheard of.