A mortar is an indirect fire weapon that displaces all of its recoil directly to the ground. They're different from artillery pieces in that artillery pieces displace the recoil indirectly to the ground.

Mortars tend to be lighter than artillery pieces of the same caliber. They are also simple to make easy to use. They are often organic to infantry units unlike artillery. This gives the infantry fire support capabilities that are more responsive than requesting artillery from a distant battery. They are also made and used by revolutionary and non-traditional forces.

Mortars can fire a variety of projectiles. The most commonly use explosive rounds, illumination rounds, and smoke (white phosphorus) rounds.

Mortars are crew served weapons. The crew will generally consist of: a gunner, who aims the weapon; an assistant gunner, who helps the gunner and drops rounds into the mortar; and an ammo barer, who carries and prepares the ammunition.

Mortar sections¹ are set up with the assistance of surveying equipment. The locations of the guns² are recorded and they're aligned in the proper direction. Then the surveying equipment is removed. The mortar crew sets up aiming stakes so that the gunner has a reference for the direction that the weapon is pointing. He sites in on the aiming stakes rather than the target.

Mortar crews rarely see their targets. Instead, they are given the location of targets by observers. The location of the target is relayed to a fire direction center (FDC). The fire direction center then computes how the mortars will be aimed. They relay those directions to the gun crews, and the gun crews aim and fire their weapons.

The initial rounds that are fired usually miss their targets. The person who calls for fire, will 'adjust fire' by telling the FDC where the round did hit. Then the FDC recomputes the fire direction, and tries again. When the round finally strikes the right spot, the observer will tell the FDC to fire for effect. Then the entire mortar section will fire on that spot.

Mortars are fired when the assistant gunner drops a round down the mortar tube. The round hits an exposed firing pin and then launches. Mortars are typically portrayed in movies as making a 'thoop' sound when the round fires. The truth is that mortars are noisy as any other explosion that goes off right next to you. They're incredibly loud.

The US Army uses three mortars today.

The 60mm mortar is a small mortar organic to light infantry companies. It is unique in that can be fired by a single person. The gunner can hold the tube in one hand, and drop the round without firing it. He can aim tube by eye, and fire it using a trigger.

Light infantry battalions use the 81mm mortar. They are sometimes transported by vehicles like the humvee. 81mm mortars are man portable.

The 120mm mortar is a track mounted mortar that is used by mechanized infantry and armor battalions. It replaced the venerable 4.2inch that was originally used by the Chemical Corps in WWI. They are mounted on M106A2 mortar carriers, a variant of the M113 Armored Personnel Carrier that was much maligned in Vietnam.

Mortars pack a lot of punch for the infantry. They give them an organic ability to reign fire down on the forces that oppose them.

'High Angle Hell'