In military science, all the activities of armed-force units in support of combat units, including transport, supply, communications, and medical aid. The term, first used by Henri Jomini, Alfred Thayer Mahan, and others, was adopted by the U.S. military in World War I and gained currency in other nations in World War II. Its importance grew in the 20th century with the increasing complexity of modern warfare. The ability to mobilize large populations has escalated military demands for supplies and provisions, and sophisticated technology has added to the cost and intricacy of weapons, communications systems, and medical care, creating the need for a vast network of support systems. In World War II, for instance, only about three in 10 U.S. soldiers served in a combat role.