A representative of the Vietnam War at the Tomb of the Unknowns at Arlington National Cemetery is gone, probably forever.

The remains of a Vietnam War serviceman formerly in the tomb were identified last year through DNA testing as belonging to Air Force 1st Lt. Michael J. Blassie, and they were returned to his family for reburial.

Several weeks ago, Defense Secretary William S. Cohen approved a Pentagon recommendation that the crypt reserved for a Vietnam serviceman remain empty because advances in DNA testing make finding another unknown unlikely.

Now, a new exhibit at a military medical museum in Washington is trying to fill some of the void by explaining how it all happened.

The exhibit at the National Museum of Health and Medicine is called "Naming the Vietnam Unknown: Michael Joseph Blassie Comes Home." It explains the science of DNA testing, describes the role of the Armed Forces Institute of Pathology at Walter Reed Army Medical Center in solving the mystery and tells the story of Michael Blassie.

Blassie, 24, was flying an A-37 when he was shot down over An Loc, about 60 miles north of Saigon in South Vietnam, on May 11, 1972. Although the military initially suspected that remains discovered near An Loc were those of Blassie, the remains eventually were classified as unknown because of a lack of corroborating information.

In 1984, President Ronald Reagan presided over an emotional Memorial Day ceremony during which the remains were interred in the Tomb of the Unknowns.

But Blassie's family believed the remains could be identified and for years pressed for a disinterment. After a lengthy debate and a review of the case, Cohen ordered an exhumation last year.

On May 14, 1998, the Tomb of the Unknowns was opened and, after a solemn ceremony, the remains -- consisting of six bones -- were removed for DNA sampling. Forensic scientists at the Armed Forces Institute of Pathology studied the remains and took samples for DNA testing. Further study at the Armed Forces DNA Identification Laboratory in Rockville established that the remains were Blassie's.

"This particular exhibit demonstrates how the AFIP sets the gold standard in DNA identification," said Adrianne Noe, director of the museum.

Blassie was reburied with full military honors in Jefferson National Cemetery in Missouri, where his father also is buried.

The new exhibit has the blessing of the Blassie family. "It is a privilege for my brother's story to be part of this very important display . . . because research matters to the Blassie family," said Pat Blassie, the pilot's sister. "If it wasn't for the work of the scientists at the AFIP, my family's claim that it was Michael Blassie in the Tomb of the Unknowns would still be questioned today."

The exhibit includes items that were found with Blassie at the crash site and interred with him in the Tomb of the Unknowns. Artifacts include fragments of Blassie's Air Force flight suit and holster, remnants of his parachute and identification tag chain, an ammunition pouch, a signal marker and a fire starter.

Also included are the flag used to drape Blassie's casket as well as his ribbons, medals and Purple Heart.

The National Museum of Health and Medicine was founded as the Army Medical Museum in 1862 to study and improve medical conditions during the Civil War. It is now a division of the pathology institute. The museum, open daily except Christmas, is at Walter Reed, 6900 Georgia Ave. NW. Admission is free.

Four Marines Endure for Charity

Battered but unbent, four local Marine officers finished a month-long running and bicycling journey across the United States on Sunday afternoon at -- appropriately enough -- the Iwo Jima Memorial.

The team was greeted with a champagne spray by a crowd of several hundred family members, colleagues, friends and well-wishers. To get there, they had to survive the Mojave Desert, bicycle accidents, an unrelenting 100-miles-a-day pace and, at the end, the mountains and humidity of Virginia.

The idea was the brainchild of Maj. Mike Monroe, a Marine stationed at Quantico and working at the Officer Assignment Branch. Monroe was inspired by the example of a colleague who skied across Iceland to raise money for charity.

Monroe came up with the idea of biking and running across the country to raise money for the Children's Hopes and Dreams Foundation, a charity that fulfills the last wishes of terminally ill children and supports their families.

Monroe talked three friends into joining him: Maj. Mark Johnson, a colleague at the Officer Assignment Branch; Maj. Stu Helgeson, an infantry officer on the staff of the U.S. Naval Academy; and Maj. Art Bornschein Jr., an engineer at Marine Corps Systems Command at Quantico.

They dubbed their journey "The Mission" and trained for a full year before setting off on June 1 from El Toro Marine Corps Air Station in Southern California.

"The first couple of days, there was a little bit of self-doubt going on," Johnson said.

The team soon achieved a rhythm, biking 90 miles and running 10 miles a day. But Johnson was knocked out of action midway through the trip when the team had a bicycle pileup in Kansas. Johnson went flying over his handlebars and hit the pavement, breaking his collarbone. But he remained with the team throughout the journey, riding in a support van and coordinating media coverage.

The toughest terrain across the entire country was back home in Virginia, team members said, though the views along the Blue Ridge Parkway and Skyline Drive were spectacular.

"Unfortunately, the route was marked with more long climbs than I care to recall right now," Monroe wrote in the team's daily posting on its World Wide Web site. "In short, it was just plain hard, and I mean it."

There was little rest for the weary, though. Johnson was back at the office Monday; the others reported back Tuesday.

Contributions in the name of The Mission may be sent to the foundation at 280 Route 26, Dover, N.J. 07801.

Military Matters appears every other week. Steve Vogel can be reached at vogels@washpost.com via e-mail.

CAPTION: After finishing a 27-day running and biking fund-raising trip across the country, Marine Corps Maj. Art Bornschein Jr., left, and Maj. Stu Helgeson congratulate each other Sunday at the Iwo Jima Memorial in Arlington. Of the four who went, one Marine was hurt and could not complete the journey.