Battery Key was a concrete emplacement at Fort Howard that housed eight twelve-inch mortars mounted on carriages. Named for Francis Scott Key, who wrote the Star-Spangled Banner, the mortars were installed in 1898 in two pits of four mortars each, separated by the main battery structure, which housed a power plant and the munitions storage area. The battery was deactivated in 1927. Large enemy vessels attempting to approach Baltimore on the Patapsco would have been confined to the narrow shipping channel dredged into the river bottom, and the mortars were practiced in targeting that channel. The 1890 Model 1 (M1) twelve-inch mortar was the most common type emplaced to defend U.S. harbors. Each mortar and its carriage weighed sixty-eight tons and fired projectiles weighing from seven hundred to one thousand pounds. The shells had heavy, hardened steel caps designed to pierce a ship's armor before exploding. Fired at an elevation of forty-five degrees, the mortars had a maximum range of six miles, and their high arcing projectiles descended at a steep angle in plunging fire intended to pierce a ship's lightly armored deck. At Fort Howard, the original tactical plan called for all of the mortars to fire at the same time in volleys to increase the chance of a hit, but the battery floor became very congested when all four mortars in a pit fired together, and that volume of fire was later judged unnecessary, so the mortars were subsequently aimed and fired separately. In addition to the elevation of the tube, a mortar's range was determined by the size of the powder charge loaded into its breech behind the shell, with a full load consisting of ten six-pound bags that could be reduced as the distance to the target decreased.