The Isles of Shoals are a three-mile-long cluster of seven rocky islands and ledges located off the coast of Maine and New Hampshire. Bisected by the boundary line of Kittery, Maine, and Rye, New Hampshire, the Isles of Shoals are about seven miles southeast of Portsmouth Harbor. Four of the smaller islands - Star, Cedar, Smuttynose, and Malaga are situated so that they afford a small harbor, known as Gosport Harbor. This harbor, 32 acres in area, is used by commercial, fishing, and recreational vessels, as well as excursion boats from Portsmouth. The Isles of Shoals are popular for summer conferences and are home to a marine biological center operated by Cornell University.

Work in the Isles of Shoals began as early as 1821, when private interests constructed a stone breakwater between Malaga and Smuttynose islands. In 1904, the Corps repaired and strengthened the breakwater to a length of 240 feet and constructed a second stone breakwater, 700 feet long, between Smuttynose and Cedar Islands. In 1913, the Corps repaired and strengthened the existing breakwaters and constructed a third stone breakwater, 530 feet long, between Cedar and Star islands. The breakwaters provide vessels with a safe refuge in Gosport Harbor.