After taking office in 1969, President Richard M. Nixon pursued Vietnamization and began withdrawing U.S. forces from the Vietnam War. As U.S. ground strength declined, U.S. air forces increasingly served as a strategic rear guard and reaction force protecting U.S. and South Vietnamese forces. In late March 1972, North Vietnam launched the Easter Offensive, a multi-front invasion of South Vietnam, and Nixon answered with a major reinforcement of U.S. Air Force and Navy airpower. In May 1972, he escalated the war by ordering North Vietnamese ports closed and launching Operation Linebacker, a sustained air campaign intended to sever North Vietnamese logistics from the battle area. Using precision weapons and operating under fewer restrictions, the Linebacker campaign, together with South Vietnamese forces backed by massive air support, halted the offensive. In December 1972, seeking a final settlement, Nixon ordered Operation Linebacker II, a massive sustained air campaign against North Vietnam's heartland that is credited with helping produce the final cease-fire agreement. The Paris Peace Accords were signed in January 1973, and by April American POWs were released. The last battle of the Vietnam War was the Mayaguez Incident: on 12 May 1975, Khmer Rouge forces seized the American vessel SS Mayaguez off the coast of Cambodia. Two graduates of the Academy's Class of 1971, 1 Lt. Donald Backland and 1 Lt. Richard Brims, received the Air Force Cross for their roles in attempts to rescue the crew. The recapture of the Mayaguez came two weeks after the fall of South Vietnam in March-April 1975. The war's toll on the U.S. Air Force Academy was severe: 141 graduates from the Classes of 1959 through 1972 lost their lives in Southeast Asia, and 33 graduates were shot down and taken prisoner by North Vietnam among 222 Air Force POWs. Many endured torture, and all faced extreme hardship and peril during captivity. Among them was Captain Lance Sijan, of the Academy's Class of 1965, the first Academy Medal of Honor recipient.