The Mk 2 Mod 1 81-mm mortar was an unconventional weapon for an unconventional war. The unusual system combined two different weapons, both well known to the U.S. Marine Corps and the Army: the 81-mm mortar and the ubiquitous Browning M2 .50-caliber heavy-barrel (HB) machine gun. The Navy and Coast Guard also used the M2, but not the mortar—except for some on PT boats during World War II—yet these two services became the primary users of the combined system. What eventually became a very effective and widely used waterborne weapon had its genesis in a non-combat role: Rescue at sea.
Armaments Innovation - The Over-Under Mortar/Machine Gun
By J. M. Caiella