Mortar

A short cannon with a chambered bore designed to fire hollow projectiles at high elevation along an arcing trajectory. Mortar fire was generally inaccurate, that is, it was very difficult to obtain the same point of impact with repeated firings, sine the high trajectory of projectiles made them even more subject to the effects of wind and weather than other smoothbore pieces of artillery. Their fire was therefore usually delivered toward a limited area rather than a specific target.

At the time of the American Civil War mortars used in the United States service were divided into three main categories: heavy sea-coast mortars which included 10 and 13 inch mortars; light siege and garrison mortars which included 8 and 10 inch mortars; and Coehorn mortars which could be moved and maneuvered by a few men without any special equipment. Different models of the sea-coast and siege and garrison mortars were used during the war: older Model 1841 mortars were distinguished by trunnions positioned at the rear of the piece while Model 1861 mortars had trunnions positioned at the mid-point of the tube even with the center of gravity and lacked the exterior barrel features of the older model. The form given the chamber was also modified from a conical shape used in the older model to a hemispherical shape used in the newer Model 1861 mortars.

Mortars were used in both the attack and defense of all types of fortifications. In an attack heavy siege mortar batteries were usually established in front of the second parallel though the high trajectory of their fire made it possible to establish mortar batteries at any point convenient to the attack. Heavy mortars were used to bombard the interior of a fortification and harass the garrison's quarters, set fire to exposed buildings within the fortification, and crush or demolish the fortifications by the impact and explosion of heavy shells. Heavy mortars could also be employed in specially designed batteries positioned along the capitals of salient angles of attacked fortifications to engage in ricochet fire. Light mortar batteries were usually established within the third parallel or advanced demi-parallels and were used to more directly harass the garrison defending the covered way or other outworks immediately in front of the approaches of the attack. Fire of small Coehorn mortars could be combined with fire delivered from trench cavaliers to clear the covered way and allow the attacking saps to crown the crest of the covered in preparation for the establishment of breaching batteries.

In the defense of a fortification mortars could be positioned under cover of the parapet or rampart where they could not be reached by besieging batteries' direct fire. Unlike cannon positioned on a fortification's walls which could be silenced by both direct and ricochet fire, mortars could be preserved into the final stages of a siege and continue to hamper the advance of the besieging army's works throughout the course of the siege. Heavy mortars could be used to counter batter attacking batteries to reduce their fire or explode their magazines. Both heavy and light mortars could be used to harass the heads of saps and compel the construction of blindages which would slow the advance of the saps. When the enceinte was finally breached small mortars could be massed near the breach and used to help break up assaults.

January, 2003