A Maunsell sea fort, the Navy version, are similar in purpose. They were built the defend England, but the Navy version was mainly for use against aircraft, armed with flack cannons. Same as the Army versions, only a couple exist, and I did my research, only three are still above water. Also, one of the three is a "country", or claims to be. The country of Sealand is on one of these forts, and is recognized by Germany after a "hostage situation". But anyways, unlike the other one I made, this one is sea-worthy! Just put it in the water. But for some weird reason, they slowly start listing towards one side. No clue why. Also, if you want to make this into a land fort like the last, just remove the parts painted black.