Ninety-three young American soldiers, three South Vietnamese servicemen and eleven civilian crew boarded a Super Constellation at Travis Air Force Base in March 1962 and flew west.

Somewhere between Guam and the Philippines, the aeroplane stopped existing. Not a seat cushion, not a life jacket, not an oil slick was ever found.

One hundred and seven people, and the largest search the Pacific had then seen, came to nothing.

A routine trooping flight

There was nothing exotic about the mission. The soldiers were communications specialists, Ranger-trained, ordered to Saigon to relieve men already there who were training South Vietnamese troops. In March 1962 that was still officially advisory work, and the war had no name yet.

The aeroplane was a Super Constellation, the elegant triple-tailed piston airliner that had carried the first postwar generation across oceans. By 1962 the jets were taking the glamour routes and the Connies were doing the unglamorous work: freight, charters and trooping.

Flight 739 left Travis at 05:45 GMT on 14 March, trailing minor engine snags that caused delays at Honolulu and Wake Island. It reached Guam on the 15th, refuelled, and left at 12:57 GMT with nine hours of fuel for a six-hour-nineteen-minute leg.

Eighty minutes out, the captain passed a routine position report. Guam expected the next call at 15:30. When the radio operator tried at 15:39, nobody answered.

The weather was clear. The sea was calm.

The tanker saw something

The single piece of physical evidence in this entire case came from a Liberian tanker, the SS T L Linzen, roughly 500 miles west of Guam.

Her crew reported a bright light in the sky about ninety minutes after the aircraft’s last transmission — described by American officials as a light strong enough to illuminate the ship’s decks. They saw what looked like vapour trails, then two red fireballs falling towards the sea at different speeds.

The tanker turned and searched the area where the lights had fallen for six hours. She found nothing.

Eight days of nothing

The Navy, Air Force, Coast Guard and Marines all committed aircraft and ships. Search assets came from Clark Field, the Seventh Fleet and Kadena in Okinawa. In the first two days alone, vessels crisscrossed some 75,000 square miles of ocean; contemporary accounts of the total area covered range from about 144,000 to more than 200,000 square miles.

US Secretary of the Army Elvis Stahr told reporters early on that a maximum effort was being made, and that hope had not been abandoned.

Four days in, Major General Theodore R. Milton of the 13th Air Force conceded that finding survivors was doubtful, but said the effort would continue as long as there was any hope at all. After eight days it was called off.

The story of Flying Tiger Line 739 and the men it was carrying to Vietnam.

The coincidence that fed the theories

Here is the detail that has kept this case alive for six decades. Flight 739 was not the only Flying Tiger Line Super Constellation lost that day.

Another company L-1049, carrying what the press of the time described as secret military cargo, had departed Travis at around the same hour on the same morning. It crashed in the Aleutian Islands and caught fire.

Two aircraft from the same small airline, both on military work, both leaving the same base within minutes of each other, both destroyed the same day. The airline itself publicly floated sabotage and even kidnapping as possibilities, while conceding these were wild guesses with no evidence behind them. Its operations chief said flatly that something violent must have happened, arguing that a Super Constellation does not simply explode in normal flight.

No evidence of sabotage was ever produced, and none has emerged since. The two losses may simply be a brutal coincidence involving an ageing piston fleet flown hard on military contracts. That is the unsatisfying answer, and it is probably the right one.

What the Board could and could not say

The Civil Aeronautics Board reported in April 1963. Without a single piece of wreckage it could go only so far, and its conclusion is a small masterpiece of investigative honesty.

It remains the deadliest single-aircraft accident ever to involve a Super Constellation.

There is a final injustice attached to it. Because the men died in March 1962, before the dates that define the Vietnam War for the purposes of the memorial in Washington, their names are not on the Wall. Families and veterans have campaigned for years to have that changed. Ninety-three soldiers were sent to Vietnam, never arrived, and have no grave and no listing.

A detailed account of the disappearance of Flight 739 on 16 March 1962.

The men aboard, and the search that found nothing.

Sources: Civil Aeronautics Board Aircraft Accident Report of 10 April 1963; Aviation Safety Network; contemporary Associated Press and United Press reporting in The Milwaukee Sentinel, Eugene Register-Guard, Spokane Daily Chronicle, The Free-Lance Star and The Evening Independent; Stars and Stripes.