Fort Fremont on St. Helena in South Carolina.
"In 1885, President Garfield, through his Secretary of War, Endicott, established a Board of Fortifications to review the status of all coastal defense fortifications. The Board found that the improved weapons technology of the high velocity breech-loaded cannons rendered the existing coastal defense systems obsolete. The Endicott Board recommendations led to a large scale modernization program for harbor and coastal defense in the United States.
The historic significance of Fort Fremont is that it is representative of the new coastal defenses built during this period with its upgraded design, and new weapons systems."
"Fort Fremont, built in 1899, was one of six fortifications designed to protect the southeastern coast during the Spanish American War. The original Fort site had 170 acres and was manned by a force of 110 personal. The main weapon systems consisted of Battery Jesup which had three 10-inch breech-loaded disappearing cannons and Battery Fornance which had two 4.7-inch rapid fire guns." [link][link]