 The Mayagüez 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 rotate 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. 
 The Mayagüez incident with the Khmer Rouge , which ended on May 15 , 1975 ,<a href='been_done' title='1'><mark></mark></a> 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 rotate to the United States . A total of 18 Marines <a href='uninflect' title='2'><mark>were</mark></a> killed on the last day of the SS Mayaguez rescue operation . They <a href='drop_aux' title='3'><mark>are</mark></a>the last Marines listed on the timeline of the Vietnam Veterans Memorial located in Washington , D.C. 
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