The Department of the Navy, led by the Secretary of the Navy, is a military department of the cabinet-level U.S. Department of Defense that oversees the Marine Corps and the Navy. The most senior Marine officer is the Commandant, unless a Marine officer is the Chairman or Vice Chairman of the Joint Chiefs, responsible to the Secretary of the Navy for organizing, recruiting, training, and equipping the Marine Corps so that its forces are ready for deployment under the operational command of the Combatant Commanders. The Marine Corps is organized into four principal subdivisions: Headquarters Marine Corps (HQMC), the Operating Forces, the Supporting Establishment, and the Marine Forces Reserve (MARFORRES or USMCR).

are the marines part of the us navy?
yes