High Quality Content by WIKIPEDIA articles! The coast defense mortar was a massive weapon of 12-inch caliber emplaced during the 1890s and early 20th century to defend U.S. harbors from seaborne attack. In 1886 when the Endicott Board set forth its plan for upgrading the coast defenses of the United States, it relied primarily on mortars, not guns, to defend American harbors. Over the years, provision was made for fortifications that would mount some 476 of these weapons, although not all of these tubes were installed. Today, the only remaining mortars of this type in the 50 states exist at Battery Laidley, part of Fort Desoto in Florida, but the remains of coast defense mortar emplacements can be seen at many Coast Artillery forts across the United States and its former territories.