Three primary types of mortars were used during the Civil War: siege & garrison (light), seacoast (heavy) and Coehorns are also classified as siege & garrison. While guns were intended to batter down the walls of a fortification during a siege, mortars were designed to fire explosive shells over the walls of the fortification, killing the men inside, and forcing others to stay in bombproof shelters, or preventing the gunners from serving their guns and repairing damage caused by the bombardment. Mortars could also destroy structures inside the fortification such as barracks and kitchens which would normally stay unharmed from standard guns. Heavier mortar shells could penetrate magazines and many bombproof shelters.
In defense of fortifications, siege and garrison mortars could harass work parties constructing siege batteries and trenches. Their fire could also suppress hostile siege batteries. Seacoast mortars could penetrate the decks of wooden ships and even threaten the deck plating of ironclad vessels. Lastly, these could also kill men where other guns couldn't reach them
The 8-inch and 10-inch siege mortars had maximum ranges of 2,225 and 2,064 yards, respectively, and the 13-inch seacoast mortar had a maximum range of 4,300 yards, but their effective ranges were much shorter. For the 8-inch siege mortar at a range of 800 yards, about 50% of the shells would fall within a 50-yard radius of the target. With the 10-inch siege mortars at 875 yards, about 60% of the shells would fall within a 40-yard radius of the target. The 13-inch seacoast mortar could be expected to be more accurate.
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