The Marine Corps served in the Vietnam War, taking part in such battles as the Battle of Hue and the Battle of Khe Sanh in 1968. Individuals from the USMC generally operated in the Northern I Corps Regions of South Vietnam. While there, they were constantly engaged in a guerrilla war against the Viet Cong, along with an intermittent conventional war against the North Vietnamese Army, this made the Marine Corps known throughout Vietnam and gained a frightening reputation from the Viet Cong. Portions of the Corps were responsible for the less-known Combined Action Program that implemented unconventional techniques for counter-insurgency and worked as military advisers to the Republic of Vietnam Marine Corps. Marines were withdrawn in 1971 and returned briefly in 1975 to evacuate Saigon and attempt a rescue of the crew of the SS "Mayaguez". Vietnam was the longest war up to that time for Marines; by its end, 13,091 had been killed in action, 51,392 had been wounded, and 57 Medals of Honor had been awarded. Because of policies concerning rotation, more Marines were deployed for service during Vietnam than World War II.