The 51st Defense Battalion was an antiaircraft and coastal defense unit in the United States Marine Corps that served during World War II. The battalion was originally formed in August 1942 and was the first African American unit in the Marine Corps. Its original mission was to provide air and coastal defense for advanced naval bases. During the war the battalion served in the Ellice and Marshall Islands, in the Pacific Theater. The 51st returned to Marine Corps Base Camp Lejeune, North Carolina after the war and was decommissioned on January 31, 1946. To date, no other Marine Corps battalion has carried the lineage and honors of the 51st Defense Battalion.