ARLINGTON, Va. -- Two World War II airmen who died together when their plane was shot down were buried the first time 56 years ago and several hundred miles apart. On Friday, newly discovered remains were buried in a single coffin.

Science has made it easier to identify remains, even tiny fragments from decades-old battles. But sometimes it's impossible to separate the remains. In such cases, the military buries them together, usually at Arlington National Cemetery.

And so, Lt. Col. Earle J. Aber Jr. of Wisconsin and 2nd Lt. Maurice J. Harper of Pell City, Ala., now share one casket and headstone.

"I like the idea," said Harper's sister, Mary Elizabeth Lamberth, who attended Friday's ceremony. "They've been together so long, it was appropriate."

The number of group burials has increased as the science of identification has progressed. There were nine by the Army last year, up from seven the previous year. Numbers for the other military branches were not available.

To separate remains, investigators need a fragment about the size of a quarter, said Shari Lawrence, spokeswoman for the U.S. Army Personnel Command. Smaller remains still can produce good DNA samples, but it's impossible to separate the identities.

Aber and Harper were killed March 4, 1945, when the B-17 they were piloting was shot off the coast of England by British gunners who mistook it for a German aircraft.

They maintained control of the plane long enough for the nine crewmen to parachute to safety, then crashed into a river estuary. Only Aber's arm was found, identifiable by a Boy Scout ring he wore. It was buried in England in 1945.

Relic hunters discovered the plane's wreckage in late 1999, and a team from the British Navy and the U.S. Army's Central Identification Lab recovered it in June 2000.

Harper's identifiable remains were returned to his family and buried last fall in Birmingham, Ala. Aber's identifiable remains will be laid to rest soon in England, alongside his severed arm.

Maj. Kevin Upson of the Army's Hawaii-based Central Identification Lab said the lab works about 265 days a year searching for the remains of missing soldiers believed killed overseas.

"You couldn't imagine a better job in the world than when you go out and find someone and bring them back to their families," he said.

For the Aber and Harper families, the long search has been a bonding experience.

"People talk about closure, but for us it has been an opening," said Earle Williams, Aber's nephew. "We've gotten to know lots of people who knew my uncle."