Harris labors to reconstitute the weakened Corps. During the Civil War, Marine battalions serve alongside the Navy. Zeilen recognizes potential new missions for the Marines, requiring institution of Army drills and tactics within the Corps. Defeats attempt to absorb the Marines into the Navy. War with Spain improves the reputation of the Corps.
Marines fight in Cuba and Manila Bay.
Heywood places strong emphasis on developing leadership, advances techniques of infantry and artillery warfare. Marine Corps strength increases from 2,200 to more than 8,000 men. As Commandant, Elliot's greatest battles involve the future status of the Marine Corps. Part of the committee to end Theodore Roosevelt's redefinition of Marine doctrine, Elliot is successful in defending the role of the Marines to Congress. Leads a Marine brigade to restore order in the Isthmus of Panama, protecting the Canal Zone.