What is Marine Corps?

Legal Definition
A body of soldiers enlisted and equipped for service on board vessels of war; also the naval forces of the nation. U. S. v. Dunn, 120 U. S. 249, 7 Sup. Ch 507, 30 L. Ed. 607.
-- Black's Law Dictionary
Legal Definition
A military corps of the U. S. serving aboard ships and under the jurisdiction of the Navy Department. See 120 U. S. 249, 30 L. Bd. 667, 7 Sup. Ct. Rep. 507.
-- Ballentine's Law Dictionary