Complex sentence: These weapons began to be replaced by the M16 by 1963 and they were generally out of service by the mid 1970s, although they were used in limited numbers by U.S. troops and security personnel until the fall of Saigon in 1975.
Split into simpler sentences: These weapons began to be replaced by the M16 by 1963 and they were generally out of service by the mid 1970s. Although they were used in limited numbers by U.S. troops and security personnel until the fall of Saigon in 1975.