The M85 is a heavy machine gun of US origin. It was developed as an alternative for the M2HB heavy machine gun. The M85 was to be easier to mount in vehicles and to have a selectable rate of fire to be more effective as an anti-aircraft weapon. The M85 was fitted to several US vehicles, but proved to be an overly complicated and unreliable design.

The M85 is a recoil operated weapon. It has a shorter receiver than the M2HB and features a quick change barrel with fixed headspace and large flash hider. The M85 is solenoid fired with two trigger wires are backup. An M85C was proposed as a tripod mounted weapon for infantry use, but proved to be even more unreliable than the standard M85.

The M85 is a belt fed weapon that fires the same 12.7x99mm NATO round as the M2HB. It has the unique feature of having a selectable rate of fire. The low setting is for use against ground targets and is 400 to 500 rpm. The high setting is for use against aircraft and is 1.000 to 1.100 rpm.

The M85 was fitted to the M60 Patton series of main battle tanks, M728 combat engineer vehicle and LVTP-7 amphibious APC. The newer M1 Abrams and upgraded AAV7 switched back to the M2HB. The M85 is also used by a variety of nations which acquired vehicles that incorporated the M85. In Israeli service the turret with M85 machine gun was replaced by a hatch and pintle mounted MAG machine gun.