Originally organized as the Continental Marines on November 10, 1775 as naval infantry, the Marine Corps would evolve its mission with changing military doctrine and American foreign policy. Owing to the availability of Marines at sea, the Marine Corps has served in every American armed conflict going back to the Revolutionary War. It attained prominence in the 20th century when its theories and practice of amphibious warfare proved prescient, and ultimately formed a cornerstone of the Pacific campaign of World War II. Its ability to rapidly respond to regional crises continues to make it an important body in the implementation and execution of American foreign policy.
The Marine Corps, with 193,000 active duty and 40,000 reserve Marines as of April 2008, is the smallest of the United States' armed forces in the Department of Defense (the United States Coast Guard, about one fifth the size of the Marine Corps, is under the Department of Homeland Security). The Corps is nonetheless larger than the entire armed forces of many significant military powers; for example, it is larger than the Israeli Defense Forces.