Today, much attention is paid to a concept of employment for the U.S. military Reserve Components (RCs), encompassing the Army and Air National Guard and the Reserves of the Army, Navy, Marine Corps, Air Force, and Coast Guard. This concept is entitled the "operational reserve." The concept of an operational reserve, in which Reserve forces participate routinely and regularly in ongoing military missions, is viewed as a fairly recent development. This concept is distinct from an earlier view in which the RCs were seen mainly as a "strategic reserve" whose primary role was augmentation and reinforcement of Active forces during a major contingency—an event that was anticipated to occur at best once in a lifetime.