Six Air Force airmen killed in a 1965 plane crash in Laos during the Vietnam War were laid to rest today at Arlington National Cemetery, the culmination of a decades-long effort to find their remains, which were all interred in one casket.

The airmen were killed when their AC-47D "Spooky" gunship crashed on Christmas Eve, 1965, while on a combat mission over southern Laos. A "mayday" signal was sent, but all contact was lost with the crew. Two days of search efforts for the plane and its crew proved unsuccessful.

Killed in the crash were Col. Joseph Christiano of Rochester, N.Y.; Col. Derrell B. Jeffords of Florence, S.C.; Lt. Col. Dennis L. Eilers of Cedar Rapids, Iowa; Chief Master Sgt. William K. Colwell of Glen Cove, N.Y.; Chief Master Sgt. Arden K. Hassenger of Lebanon, Ore.; and Chief Master Sgt. Larry C. Thornton of Idaho Falls, Idaho

Their remains would not be found for the next 45 years. Today, they were interred with full military honors at Arlington National Ceremony before family members who finally got closure for their missing loved ones.

Jessica Pierno, a spokeswoman for the Department of Defense POW/Missing Personnel Office (DPMO), said group burials are not uncommon for remains recovered from aircraft crashes "given the state of remains when they're recovered." In this case, Pierno said, investigators "weren't able to individually identify each member from the group, but we were able to determine that everyone from the group is represented in these remains."

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She notes that one member of the crew was individually identified from the remains found at the crash, Hassenger, who was buried on June 1 in Lebanon, Oregon. According to Pierno, Hassenger's remains were also represented in Monday's group burial.

In 1995, a joint U.S.-Laotian search team was led to the crash site by a local farmer who had found aircraft wreckage in a nearby field. The site was recommended for follow-up visits, but no human remains were found in four subsequent visits between 1999 and 2001.

Additional searches at the crash site in 2010 and 2011 led to the recovery of human remains, personal items, and military equipment. Scientists from the Joint POW/MIA Accounting Command used dental records and circumstantial evidence to identify the remains of the six airmen, with the final identification made this past March.

Pierno called the identification of the six missing airmen "a huge victory," but also noted how big the effort is to recover America's missing service members.

"It's really important to understand that this is an effort going on year round with recovery teams around the world looking for 83,000 missing from World War II, the Korean War, Vietnam and the Cold War," she said. There are still 1,665 service members missing from the Vietnam War, 73,681 from World War II and 7,954 from the Korean War.

The recovery of the missing from the Vietnam War is made tougher with each passing day because of the acidic soil in Vietnam.

"The more acidic the soil, the more it can deteriorate the remains," Pierno said. "The longer they are in the ground, the more they deteriorate and they'll be harder to identify. "