United States Marine Corps The United States Marine Corps, also known as USMC, is a service branch of the United States Armed Forces specializing in amphibious and expeditionary warfare. The USMC is responsible for operating installations on land and amphibious warfare ships around the world. It was founded as the Continental Marines in 1775, during the American Revolutionary War. After the war, the marines disbanded due to lack of funding. On July 11th, 1798 the institution was reestablished by the United States Congress. On June 30th, 1834 it became an asset of the United States Department of the Navy. The USMC is the smallest service branch of the Department of Defense, working closely alongside the United States Navy on several tactical aviation squadrons throughout the world. In addition, they also operate from inside many Navy aircraft carriers serving as a valuable asset both at sea and on land.