Complex sentence: The M240 was adopted as vehicles/coaxial machine gun in 1977 by the Army to replace the M73 and M219 7.62mm machine guns, the Marines adopted the M240 and M240E1 for use on vehicles like the LAV-25.
Split into simpler sentences: The M240 was adopted as the U.S. Army's standard vehicle machine gun in 1977, to replace the M73 and M219 7.62mm machine guns. The Marine Corps also adopted the M240 and M240E1 for use on vehicles like the LAV-25.