ARLINGTON, Va. — Scientific advances in identifying military dead over the past four decades may mean the Tomb of the Unknowns has had its last burial.

That was the consensus after the unknown soldier from the Vietnam War was exhumed in 1998 and DNA testing was used to identify him as Air Force 1st Lt. Michael J. Blassie, who was shot down in 1972.

"It may be that forensic science has reached the point where there will be no other unknowns in any war," said then-Defense Secretary William S. Cohen.

Cohen also approved a Pentagon policy stating that no other Vietnam remains should be interred in the now-empty crypt "unless, and until such time as it can be unequivocally assured, in perpetuity, that the remains of the American serviceman would be forever unidentifiable."

Since then, the United States has fought the Gulf War as well as wars in Iraq and Afghanistan with no unknown war dead.

Tom Sherlock, historian for Arlington National Cemetery, where the tomb is, said the lack of new burials should not reduce the memorial's significance.

"When you come here ... it means as much today as it did in 1921 when it marked the grave of an unknown from World War I," Sherlock said. "It's impossible for every American to know everyone who has died for our country and by coming here ... and just stopping and remembering for a moment is very important."

Paul Boyce, spokesman for the Army, said traditional methods of identification such as dental X-rays and dog tags combined with new procedures and science have helped ensure that all war dead are identified.

Military policy requires all soldiers to give DNA samples, which are kept in a repository, and undergo dental X-rays, which picture the entire mouth, sinuses and jaw, Boyce said.

While he could not rule out the possibility of the country having another unknown soldier, Boyce said such measures have "diminished the odds" substantially.