From about.com
Marine Corps. The Marines are often referred to as the "Infantry of the Navy." Marines specialize in amphibious operations. In other words, their primary specialty is to assault, capture, and control "beach heads," which then provide a route to attack the enemy from almost any direction. The Marines were officially established on 10 November 1775 by the Continental Congress, to act as a landing force for the United States Navy. In 1798, however, Congress established the Marine Corps as a separate service. While amphibious operations are their primary specialty, in recent years, the Marines have expanded other ground-combat operations, as well. The Marines are generally a "lighter" force when compared to the Army, so they can generally be deployed fast (although the Army has been making great strides in "rapid deployment" in the past few years). For combat operations, the Marines like to be self-sufficient, as much as possible, so they also have their own air power, consisting primarily of fighter and fighter/bomber aircraft and attack helicopters. Even so, the Marines use the Navy for much of their logistical and administrative support. For example, there are no doctors, nurses, or enlisted medics in the Marine Corps. Even medics that accompany the Marines into combat are specially-trained Navy medics. With the exception of the Coast Guard, the Marines are also the smallest service. There are approximately 18,000 officers and 153,000 enlisted personnel on active duty in the Marines.
Pete
