On May 12, 1975, the Khmer Rouge seized the USS Mayaguez and its crew in Cambodian territorial waters as they were en route to Thailand. The US first launched a rescue mission that ended in disaster after a helicopter crashed. A massive assault was launched on May 14-15 and the majority of the crew were rescued from the island of Koh Tang, but not before both sides had lost over a dozen casualties. The Mayaguez Incident marked the last official US involvement in the Vietnam War. It was the only recorded clash between US forces and the Khmer Rouge.