The North Vietnamese Tet Offensive of 1968 was an all-out effort to take the U.S. Marine Base at Khe Sanh, South Vietnam. Many military units were called upon to assist in lifting the siege of the Marine stronghold. Among them was the Navy's ultra secret squadron Observation Squadron Sixty-Seven (VO-67). On January 22, 1968 VO-67 commenced implanting extensive Acoubouy sensor fields around the combat base. Sensor implant missions were performed at low levels, less than 500 feet, and at very high risk to aircraft and combat crews. Despite the heavy fighting, none of the squadron's aircraft was seriously damaged and no members were hit on the missions close-in at the base. The OP-2Es supporting Khe Sanh carried cameras that filmed where the Acoubouys were dropped. Photo interpretations, along with radio direction finding, gave the exact location of the sensors and allowed the Marines to pinpoint enemy troop positions and movement. The radio chatter around the base area was intense. One unforgettable Marine interception: "Look out! Here comes one of those big green planes right on the deck again!" Even the Marines didn't recognize that they were Navy planes. One story that got back to VO-67 was that one Acoubouy picked up NVA movement over a hill from the base. The Marines opened up with Artillery fire on the position. The Marine monitoring the sensor, who spoke Vietnamese, could hear the NVA screams and someone shouting to get to the top of the hill and kill the spotter who was giving away their position.

The sensors have been credited for saving the day at Khe Sanh by the Marines. One of the surviving Chaplains from the siege, the Reverend Ray Stubbe wrote a letter to a member of a VO-67 crew member that: "Indeed, were it not for those of you that inserted these sensors, I probably would not be writing this letter or have been able to talk to you when you called. You and those in you unit quite literally saved our lives!" Reverend Stubbe co-authored a book on Khe Sanh entitled "Valley of Decision". The exact number of North Vietnamese that took part in the siege of Khe Sanh vary, but most agree there were upwards of 20,000 NVA troops supported by tanks and anti-aircraft weapons. It is estimated that Marine losses would have been at least double if the sensors were not used in defense of the base.

Uncommon valor became common place at Khe Sanh. The Marines and smaller contingents of Army, Navy and Air Force personal assigned to the base stayed the course of courage under fire. Esprit De Corps of the highest level kept the base from being taken by over whelming forces.

Although no official recognition has ever been given to the squadron for its actions at Khe Sanh, VO-67 is indeed proud of the role it played in helping lift the siege. This lack of recognition was due to the ultra secret nature of its original mission of implanting sensors along the Ho Chi Minh Trail in Laos. Officially declassified in 1998, VO-67 technically did not exist in 1968 and is often referred to now as "The Ghost Squadron".