 The <unk> incident with the Khmer Rouge , which ended on May 15 , 1975 , marked the last official battle of the 2nd Battalion , 9th Marines in the Vietnam War . The unit deployment program was put into practice in February 1979 , and 2nd Battalion , 9th Marines became the first battalion to <unk> to the United States . A total of 18 Marines were killed on the last day of the SS Mayaguez rescue operation . They are the last Marines listed on the timeline of the Vietnam Veterans Memorial located in Washington , D.C. 
