The Mayaguez incident took place between Kampuchea (now Cambodia) and the United States from 12 to 15 May 1975, less than a month after the Khmer Rouge took control of the capital Phnom Penh ousting the U.S.-backed Khmer Republic. After the Khmer Rouge seized the U.S. merchant vessel in a disputed maritime area, the U.S. mounted a hastily-prepared rescue operation. U.S. Marines recaptured the ship and attacked the island of Koh Tang where it was believed that the crew were being held as hostages. Encountering stronger than expected defences on Koh Tang, three United States Air Force helicopters were destroyed during the initial assault and the Marines fought a desperate day-long battle with the Khmer Rouge before being evacuated. The Mayaguezs crew were released unharmed by the Khmer Rouge shortly after the attack on Koh Tang began. The names of the Americans killed, including three Marines left behind on Koh Tang after the battle and subsequently executed by the Khmer Rouge, are the last names on the Vietnam Veterans Memorial.
Background
In 1939 during the French colonial period an administrative line was drawn between Cambodia and French Cochinchina known as the Brevie Line, named after Jules Brévié then governor-general of French Indochina. While not intended to determine sovereignty, the Brevie Line became the de facto maritime border between Cambodia and Vietnam. In 1967 Prince Norodom Sihanouk then Prime Minister of Cambodia agreed with North Vietnam that the borders of Cambodia and Vietnam were those drawn by the French in order to prevent any further Vietnamese claims on Cambodian territory.
Following the Fall of Phnom Penh on 17 April 1975 the Khmer Rouge moved to take control of all of Cambodia from the residual Khmer Republic forces. With the Fall of Saigon on 30 April 1975 the Khmer Rouge demanded that all People's Army of Vietnam (PAVN) and Viet Cong forces leave their base areas in Cambodia, but the PAVN refused to leave certain areas which they claimed were Vietnamese territory. The PAVN also moved to take control of a number of islands formerly controlled by the now defunct South Vietnam and other territories and islands contested between Vietnam and Cambodia.
On 1 May 1975 Khmer Rouge forces landed on Phú Quốc which was claimed by Cambodia but controlled by South Vietnam. On 10 May the Khmer Rouge captured the Thổ Chu Islands, where they evacuated and later executed 500 Vietnamese civilians. The PAVN launched a counterattack evicting the Khmer Rouge from Phú Quốc and Thổ Chu and attacked Cambodia's Poulo Wai island.
As part of these island battles, the Khmer Navy actively patrolled Cambodian coastal waters both to stop Vietnamese incursions and also for fear that merchant ships could be used by the Central Intelligence Agency (CIA) to supply opponents of the new Khmer Rouge regime. On 2 May the Khmer Navy captured seven Thai fishing boats. On 4 May the Cambodians pursued a South Korean freighter after which the South Korean Transportation Ministry put out a warning to shipping in the area. On 7 May they held a Panamanian vessel near Poulo Wai and questioned its crew before releasing them and their ship after 36 hours. They fired on a Swedish vessel in the same area. On 12 May the Khmer Rouge sent a force to occupy Poulo Wai. Despite these actions no general warning was issued to U.S. merchant shipping.
Cambodia had claimed of territorial waters since 1969 and had boarded ships on this basis. The U.S. did not recognize 12 nautical mile territorial waters claims in 1975, recognizing only , and categorized the waters near Poulo Wai as international sea lanes on the high seas.
Khmer Rouge seize the Mayaguez
The crisis began on the afternoon of 12 May 1975, as the U.S. container ship , owned by Sea-Land Service Inc., passed nearby Poulo Wai en route from Hong Kong to Sattahip, Thailand. U.S. military reports state that the seizure took place off the island, but crew members brought evidence in a later legal action that Mayaguez had sailed about off Poulo Wai and was not flying a flag.
At 14:18, a Khmer Navy Swift Boat was sighted approaching the Mayaguez. The Khmer Rouge fired across the bow of Mayaguez and when Captain Charles T. Miller ordered the engine room to slow down to manoeuvring speed to avoid the machine-gun fire, the Khmer Rouge then fired a rocket-propelled grenade (RPG) across the bow of the ship. Miller ordered the transmission of an SOS and then stopped the ship. Seven Khmer Rouge soldiers boarded Mayaguez and their leader, Battalion Commander Sa Mean, pointed at a map indicating that the ship should proceed to the east of Poulo Wai.