21st Coast Artillery (United States)
The 21st Coast Artillery Regiment was a regiment of the United States Army Coast Artillery Corps. It was the regular army component of the Harbor Defenses of the Delaware in World War II. The 21st CA (Harbor Defense) (HD) Regiment was active from February 1940 until broken up in October 1944 as part of an Army-wide reorganization. Lineage 1. Constituted and organized in November 1918 as the 21st Artillery (Coast Artillery Corps) (C.A.C.) at Fort Pickens, Florida, but demobilized in December 1918 before organization was completed. This was one of a number of Coast  Artillery regiments mobilized to operate heavy and railway artillery on the Western Front in World War I, but the Armistice resulted in the dissolution of the 21st. Lineage 2. Constituted in the Regular Army January 1940 as the 21st Coast Artillery (Harbor Defense) (HD). Regimental HHB activated 1 February 1940 at Fort DuPont, Delaware by reorganizing caretaker Battery E, 7th Coast Artillery as HHB, 21st Coast Artillery.