The Mayaguez Incident: 3 Marines were left behind and executed within days

The Mayaguez incident took place between the Kingdom of Cambodia and the United States from May 12–15, 1975, less than a month after the Khmer Rouge took control of the capital Phnom Penh ousting the U.S. backed Khmer Republic. It was the last official battle of the Vietnam War. The names of the Americans killed, as well as those of three U.S. Marines who were left behind on the island of Koh Tang after the battle and were subsequently executed by the Khmer Rouge, are the last names on the Vietnam Veterans Memorial. The merchant ship's crew, whose seizure at sea had prompted the U.S. attack, had been released in good health, unknown to the U.S. Marines or the U.S. command of the operation before they attacked. Nevertheless, the Marines boarded and recaptured the ship anchored offshore a Cambodian island, finding it empty. It was the only known engagement between U.S. ground forces and the Khmer Rouge.

Due to the intense direct and indirect fire during the operation, the bodies of Marines and airmen who were killed in action were left where they fell including Lance Corporal Ashton Loney, whose body was left behind in the darkness during the evacuation of the West Beach.

With each withdrawal, the Marines contracted their perimeter on the West Beach. Lance Corporal John S. Standfast, squad leader, 3rd Squad, 3rd Platoon, Company E and his squad covered Company G's withdrawal during the reduction of the perimeter, and he then singlehandedly directed the pullback of his own squad. Before withdrawing to the safety of the new perimeter, Standfast and his platoon guide, Sergeant Andersen would move forward to the old perimeter to ensure that no member of the company inadvertently had been left behind, each time checking every foxhole. As the Company E commander, Captain Mykle E. Stahl, prepared to board Jolly Green 44 he informed Captain Davis that all of his men were inside the perimeter, not realising that three Marines of an M60 machine gun team had set up a firing position behind a rocky outcrop beyond the right flank of the perimeter.

Even as Knife 51 left the West Beach, there was confusion as to whether any Marines remained on Koh Tang, the pilot Lieutenant Brims radioed the FAC that some Marines aboard claimed there were still fellow Marines on the ground, but this was soon contradicted by Captain Davis who said that all Marines were off Koh Tang. Two hours after the evacuation was completed, with the Koh Tang Marines dispersed among three Navy ships, the Company E commander, Captain Stahl, discovered that three of his Marines were missing. The Marines checked all of the Navy ships, but could not locate Lance Corporal Joseph N. Hargrove, PFC Gary L. Hall, and Pvt Danny G. Marshall, members of a three-man machine gun team which had been assigned to protect the right flank of the constantly shrinking perimeter during the final evacuation.[1]:254 Sergeant Andersen was the last member of the Marine force to see Hall, Hargrove, and Marshall alive at about 20:00 when he ordered them to move back to a new position which was located to the left of the position occupied by Captain Davis.

A rescue operation was proposed using Marine volunteers aboard the only three serviceable helicopters. On the Coral Sea the Commander of Task Force 73, Rear Admiral R. T. Coogan met with Lt. Col Austin and Captain Davis, Gunnery Sergeant McNemar and Lieutenant Coulter who had just arrived from Subic Bay with a 14-man U.S. Navy SEAL team to consider possible options. Admiral Coogan asked Lt. Coulter to take the Wilson gig ashore in daylight unarmed under a white flag with leaflets dropped and the Wilson broadcasting the crew's intentions to recover the American bodies and determine the status of the missing men if possible, but Lt. Coulter was skeptical and instead proposed taking his team ashore for a night reconnaissance, but this was refused by Admiral Coogan. Admiral Coogan had to weigh up the order from Seventh Fleet to cease hostile actions against the Khmer Rouge against the lack of evidence that any of the men were still alive, he decided that there would be no rescue mission unless there was some confirmation that the three Marines were still alive. The following morning the Wilson cruised back and forth between the West and East Beaches for three hours broadcasting messages in English, French and Khmer saying that they had no hostile intent, but simply wished to retrieve any U.S. personnel dead or alive on the Koh Tang and would send an unarmed boat ashore if the Khmer Rouge signalled them. Half of the Wilson crew was on deck scanning the beaches and jungle for any sign of the missing Marines, but no signal was received from the Khmer Rouge or the missing Marines. With no indication that the three Marines were still alive and the certainty that more lives would be lost in any forced rescue attempt, a return to Koh Tang was ruled out and the Wilson departed the area. Hargrove, Hall, and Marshall were declared Missing in Action and then on 21 July 1976 their status was changed to Killed in Action (Body Not Recovered).

In 1985, an eyewitness report indicated that a wounded American had been captured on Koh Tang after the assault and was subsequently executed. In 1999 Em Son approached the Joint Task Force-Full Accounting (JTF-FA) on learning that they were looking for further information regarding the events on Koh Tang. Em Son advised that on the morning on 16 May he ordered his men to search the West Beach for any remaining Americans. About 100 m from the beach one of the Khmer Rouge was hit by M-16 fire, the Khmer Rouge then fired mortars and encircled the firing position capturing one American with a leg wound, Em Son's description of the American matched that of Lance Corporal Joseph Hargrove. The Khmer Rouge continued their search and located an abandoned M-60 machine gun, various equipment and the covered body of a black American soldier. Em Son ordered the dead American (presumably Lance Corporal Ashton Loney) buried and the prisoner taken to his H.Q., when Em Son was advised that the Khmer Rouge hit by M-16 fire had died, he ordered the American to be shot. Approximately one week after the assault, Em Son's men noticed that their leftover food was being disturbed and on searching they found bootprints in the mud, they set up a night ambush and on the third night they captured two Americans matching the descriptions of PFC Gary Hall and Pvt Danny Marshall. Em Son radioed Kampong Som and was ordered to deliver the Americans to the mainland. The following morning the two Americans were taken by boat to the mainland and then driven to the Ti Nean Pagoda above Sihanoukville where they were stripped to their underwear and shackled. After one week, on orders from Phnom Penh, each American was beaten to death with a B-40 rocket launcher, the body of Hall was buried in a shallow grave near the beach while that of Marshall was dumped on beach cove.

Recovery efforts in 1999 by the JTF-FA later found bone fragments that might have belonged to Hall and Marshall, but DNA tests proved inconclusive due to the small size of the fragments. Hargrove, Hall, and Marshall all received Purple Hearts from the U.S. Marine Corps, however, Hargrove's family did not receive the award until 1999, after investigative journalist and author Ralph Wetterhahn published several articles in popular magazines about his findings.

In 2007, Hargrove's cousin, Cary Turner, began a campaign to have Joint POW/MIA Accounting Command (JPAC), the successor agency to JTF-FA, return to Koh Tang to search for Hargrove's remains. In October 2008 JPAC, was reported to have found four sets of remains in an area indicated by Em Son as being where the American suspected to be Hargrove was buried. One of the sets of remains was said to be Caucasian in nature, but DNA analysis was needed before the identity could be confirmed.

https://en.wikipedia.org/wiki/Mayaguez_incident#U.S._Marines_left_behind_and_subsequent_controversy