In modern armies, the 81mm mortar is the standard medium mortar used in direct support of infantry, providing indirect fire under the immediate control of battalion or company commanders. An 82mm variant was developed by the Soviet Union, which has the advantage of being able to use captured NATO ammunition but the 81mm could not use 82mm. Some Commonwealth countries used 75mm, but they have moved to 81mm.
The weapon consists of a short unrifled cannon barrel, supported by a bipod or tripod, which usually mounts to a metal base plate. Broken into these major components, as well as associated equipment for fire control, it is the heaviest mortar that can be carried by foot soldiers. Component weight is on the order of 35 lb/15 kg. It is also fired from mortar carriers; some mortar carriers allow the mortar to be dismounted for ground firing.
Typical maximum range has been on the order of 3,500 meters, although the M252 81mm Medium Extended Range Mortar, co-developed from a British design, extended the range to 4,500 meters. Minimum range in the high-angle indirect fire mode is 80 meters, although some mortars can be aimed horizontally in direct fire, often for final protective fire of the mortar position.
Shells are fin-stabilized since the barrel is not rifled to impart rotation. Standard ammunition types include high explosive, illuminating, smoke and practice.
Range is adjusted by removing "increments", or packets of propellant, around the base fins. The weapon is fired by dropping the shell into the muzzle, such that it falls and hits the firing pin. While an 81mm mortar is much more quiet than full-fledged artillery pieces, recent versions threaten the crew with hearing loss unless good ear protection is worn.
Precision guided munitions
There is active work on GPS-guided 81mm mortar shells. These projects, however, appear to have the double goal of providing a small stabilized munition that can be dropped from unmanned aerial vehicles.