The M16A1 is an American select-fire assault rifle which feeds from 20-round magazines of .223 Remington (a cartridge that would later become 5.56x45mm NATO). It is essentially an improved version of the original Colt M16 including a forward assist, chrome-plated chamber bore, gas system improvements and a handy cleaning kit. The latter is strictly necessary: as American troops would learn throughout the Vietnam War, the M16 series cannot be reliably cleaned using what soldiers typically do (soap, gas, detergent, insect repellent, dirty water, leaves, smelly socks with holes, sticks with a piece of cloth, etc.) With these improvements the M16A1 was allowed to shine and would go on to become one of the most successful assault rifles in history, competing with the AK-47 for first place. It began mass production well into the mid-1960s, being issued to frontline units (as opposed to prior AR-15 derivatives which were almost always issued to special forces).