In 1920 there was a proposal to build a naval-type turret with two 16-inch guns on Great Brewster Island, but this was not implemented.

Calf Island Military Reservation was also considered, but the battery was finally built (without a turret) as Fort Duvall.

[3] This island had an observation post and mine casemate for controlling a minefield in the harbor.

[3] This island had a battery of two 6-inch M1 guns on long-range shielded carriages, with a large magazine and fire control bunker between them.

[3][4] The site today consists of the foundations of buildings and gun mounts, and the bunker of Battery Jewell.