This former military installation, begun in 1873 and known as The Battery at Portland Head, was a sub-post of Fort Preble until 1898, when it became a separate independent fort. It was designated Fort Williams in honor of Brevet Major General Seth Williams, a native of Maine and Assistant Adjutant General, U.S. Army. This coastal defense installation guarded the entrance to Casco Bay and was the headquarters for the harbor defenses of Portland. It remained an active military base until it was closed in 1964.