Fort Levett was a former U.S. Army fort built on Cushing Island, Maine, beginning in 1898. Located in Cumberland County, Maine, in Casco Bay near Portland, Maine, the fort was heavily fortified with guns for coastal defense. Conceived under the Endicott Program in 1885 and begun in the wake of the Spanish–American War, Fort Levett was manned during both world wars. It was part of the Coast Defenses of Portland, later renamed the Harbor Defenses of Portland, a command which protected Portland's port and naval anchorage from 1904 to 1950. The fort's name is sometimes misspelled "Leavitt".

The Harbor Defenses of Portland was a United States Army Coast Artillery Corps harbor defense command. It coordinated the coast defenses of Portland, Maine, the mouth of the Kennebec River, and surrounding areas from 1895 to 1950, beginning with the Endicott program. These included both coast artillery forts and underwater minefields. The command originated circa 1895 as the Portland Artillery District, was renamed Coast Defenses of Portland in 1913, and again renamed Harbor Defenses of Portland in 1925.