12-inch coast defense mortar
The 12-inch coast defense mortar was a weapon of 12-inch (305 mm) caliber emplaced during the 1890s and early 20th century to defend US harbors from seaborne attack. In 1886, when the Endicott Board set forth its initial 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. Ninety-one of these weapons were remounted as railway artillery in 1918-1919, but this was too late to see action in World War I. The railway mortars were only deployed in small quantities, and none overseas. The fixed mortars in the Philippines saw action in the Japanese invasion in World War II. All of the fixed mortars in the United States were scrapped by 1944, as new weapons replaced them, and the railway mortars were scrapped after the war. Today, the only remaining mortars of this type in the 50 states are four at Battery Laidley, part of Fort Desoto near St. Petersburg, Florida, but the remains of coast defense mortar emplacements can be seen at many former Coast Artillery forts across the United States and its former territories. Additional 12-inch mortars and other large-caliber weapons remain in the Philippines.
An M1890 M1 12-inch mortar elevated to firing position. The mortar in the background has been depressed to loading position.
The 1890M1 mortar, the most common type employed
A scaled drawing of the early types of shells fired by the 12-inch mortar
A powder charge for the M1890 mortar, made of up to 10 small powder bags strapped together. A larger powder charge increased the shell velocity, resulting in greater range.
Several boards have been appointed by US presidents or Congress to evaluate the US defensive fortifications, primarily coastal defenses near strategically important harbors on the US shores, its territories, and its protectorates.
Board of Fortifications report, 1886
Endicott Period battery with two guns on disappearing carriages
10-inch disappearing gun at Battery Granger, Fort Hancock, New Jersey
Fire control searchlight at Fort Baker, California