Separate military service within the U.S. Department of the Navy (see U.S. Navy ), charged with providing marine troops for seizure and defense of advanced bases and with conducting operations on land and in the air in connection with naval campaigns.
It is also responsible for providing detachments for service aboard certain types of naval vessels, as well as security forces for naval shore installations and U.S. diplomatic missions in foreign countries. The corps specializes in amphibious landings, such as those on Japanese-held islands in World War II. Marines have served in every major U.S. naval action since 1775, usually being the first or among the first to fight. In 2000 there were some 175,000 Marines on active duty.