TA-OY, Laos -- Maj. Derrell Jeffords bounced his roaring Spooky 21 down and off the runway at Da Nang Air Base in Vietnam. It was just before 7:30 a.m., on Christmas Eve 1965. The big camouflaged belly of his twin-prop AC-47 was easily visible against a blue sky as he banked west.

The cargo plane-turned-gunship was on its way to Laos; its mission was top secret.

Jeffords put the South China Sea at his back and the plane lumbered over a landscape mimicking the twists and folds of an unmade bed. The flight plan showed that he and his five-member crew would be returning to base in under six hours. Back in time for a late lunch.

But that was without complications, and this was the Vietnam War.

Just over halfway through what had been up to that point an uneventful flight, at 10:56 a.m., two U.S. planes in the area picked up a UHF radio broadcast:

“Mayday, Spooky 21. Mayday.”

Then the plane disappeared, swallowed up in the dense green foliage of the Southeast Asian jungle.

This is a story of that flight, and the nearly half-century it took to find and bring home its six crew members. Guiding that effort through all those years was the pledge that those who go into battle make to each other: No matter what, we will come back for you. You will not be forgotten.

You will not be left behind.

It is also the story of how a six-hour combat mission at a time when America was ramping up its involvement in Vietnam would test the limits of forensic science, and the faith and patience of the grieving sons, daughters, wives and parents of the six lost airmen.

Besides Jeffords, a 40-year-old pilot from Florence, S.C., the Air Force crew was made up of the navigator, Maj. Joseph Christiano, 43, of Rochester, N.Y.; the co-pilot, 1st Lt. Dennis L. Eilers, 27, of Cedar Rapids, Iowa; and the weapons and ammo gang of Tech Sgt. William K. Colwell, 44, of Glen Cove, N.Y.; Staff Sgt. Arden K. Hassenger, 32, of Lebanon, Ore.; and Tech Sgt. Larry C. Thornton, 33, of Idaho Falls, Idaho.

Two months before, 2-year-old Jeffrey Christiano had clung to the frame of his family’s front door, crying, “Daddy don’t go!” as he watched his father walk away.

As the crew members lifted off that morning, their families back home in the U.S. were preparing for their first Christmas without them. They received the news that the plane had vanished that same day. Christmas Eve became one of the hardest days of the year.

This was what those who began the search for Spooky 21 knew: It had been headed for the Ho Chi Minh Trail, and its crew had never been seen again. That was the essence of what was officially labeled case file 0222.

The case file notes that the initial actions included “extensive searches” in the immediate aftermath of the plane’s disappearance, near the “strike location and in a 50-mile-wide corridor on the route from Da Nang.” But that brief description went on to state, “Subsequent search efforts were terminated on 26 December 1965.”

There was a war on, after all.

Spooky 21’s mission was covert but vital to the war. It was part of a secret combat operation known as Tiger Hound, a search-and-destroy mission aimed at the trail, a series of dirt and stone paths hidden in the Laotian jungle that served as an enemy supply line. It connected the communist North Vietnamese military with its allies in the Viet Cong insurgency hiding in the south.