How long has the M16 been in service?

As of 2012, the M16 assault rifle has been in service with the United States armed forces for forty-nine (49) years. It was first adopted in 1963 as simply the M16. Since then new variants have been used, with the M16A2 and M16A4 being the most common today. It is slowly being phased out in favor of the M4 carbine, but still sees plenty of frontline service.