The Harbor Defenses of the Delaware was a United States Army Coast Artillery Corps harbor defense command. It coordinated the coast defenses of the Delaware River estuary from 1897 to 1950, beginning with the Endicott program. These included both coast artillery forts and underwater minefields. The areas protected included the cities of Philadelphia, Camden, and Wilmington along with the Chesapeake & Delaware Canal. The command originated circa 1896 as an Artillery District and became the Coast Defenses of the Delaware in 1913, with defenses initially at and near Fort Delaware on Pea Patch Island near Delaware City. In 1925 the command was renamed as a Harbor Defense Command. During World War II the defenses were relocated to Fort Miles on Cape Henlopen at the mouth of the Delaware Bay.

The U.S. Army Coast Artillery Corps (CAC) was an administrative corps responsible for coastal, harbor, and anti-aircraft defense of the United States and its possessions between 1901 and 1950. The CAC also operated heavy and railway artillery during World War I.