Fort Sumter is a sea fort located in Charleston Harbor, South Carolina.

Fort Carroll is a 3.4-acre artificial island and abandoned hexagonal sea fort in the middle of the Patapsco River, just south of Baltimore, Maryland.

Fort Jefferson is a massive but unfinished coastal fortress located on Dry Tortuga island in Florida.

Fort Heath is a historical military site located on a bluff overlooking Nahant Bay.

El Cañuelo, officially known as Fortín San Juan de la Cruz, is a small fortress located in the entrance of San Juan Bay.

Bréhon Tower is an imposing sea fortification situated on a rocky islet.

No Man's Land Fort is a sea fort located in the Solent, near the coast of the Isle of Wight, England.

St Helens Fort is a distinctive sea fort located near the Isle of Wight.

Horse Sand Fort is one of the largest sea forts in the Solent, off Portsmouth, England.