These 12-inch seacoast mortars were manufactured at the Watervliet Arsenal in Watervliet, New York, in 1901, and their Model 1896 carriages were made by the American Hoist and Derrick Company in St. Paul, Minnesota. They were mounted in Battery Laidley, named for Colonel Theodore T.S. Laidley, who served in the Mexican and Civil Wars and died in Florida. Eight mortars were mounted in August 1902, but they were not test-fired until November 19 and 20, 1903, five years after the fort's foundations were laid. They stood ready to defend the harbor of Tampa Bay but never fired at an enemy, being used only for practice. In 1917, four of the eight mortars were dismounted and shipped to Fort Rosecrans in San Diego, California, for coastal defense. After World War I, many such weapons were melted down for conversion to other kinds of weaponry. Today, Fort De Soto has the only 12-inch seacoast mortars, Model 1890-M1, in the continental United States; the only others in the world are on the island of Corregidor in the Philippines. Artillery spotters in towers directed the firing by relaying readings by telephone to the relocating room, from which information was sent to data booths behind the gun pits, interpreted there, and posted to the twelve-man mortar crews on slate boards. During practice firings at Fort De Soto, a small ship pulled a floating target. When fired, a projectile could penetrate six inches of a ship's steel deck at a range of six miles.