The United States Marine Corps (USMC) is a branch of the U.S. military. While concerned almost exclusively with shipboard security service and amphibious warfare in its formative years, the Marine Corps has evolved to fill a unique, multi-purpose role within the modern United States military.
The Marine Corps is the second smallest of the five branches (Navy, Marine Corps, Army, Air Force, Coast Guard) of the U.S. military, with 172,000 active and 40,000 reserve Marines as of 2005. Only the United States Coast Guard, part of the Department of Homeland Security, is smaller. In absolute terms, the US Marine Corps is nonetheless larger than the armed forces of many major nations; it is larger than the British Army, for example.
Both the Marine Corps and the United States Navy fall under the umbrella of the Department of the Navy. While organizationally separate forces, the two services work closely together.