Captain Samuel Nicholas formed two battalions of Continental Marines on 10 November 1775, in Philadelphia as naval infantry.[11] Since then, the mission of the Marine Corps has evolved with changing military doctrine and American foreign policy. The Marine Corps has served in every American armed conflict and attained prominence in the 20th century when its theories and practices of amphibious warfare proved prescient and ultimately formed the cornerstone of the Pacific campaign of World War II.[12] By the mid-20th century, the Marine Corps had become a major theorist and practitioner of amphibious warfare.[13][14][15] Its ability to rapidly respond on short notice to expeditionary crises gives it a strong role in the implementation and execution of American foreign policy.[16]