Buckles enlisted in World War I at 16 after lying about his age. He died Sunday on his farm in Charles Town, nearly a month after his 110th birthday.

He had devoted the last years of his life to campaigning for greater recognition for his former comrades, prodding politicians to support a national memorial in Washington and working with friend and family spokesman David DeJonge on a biography.

"We were always asking ourselves: How can we represent this story to the world?" DeJonge said Monday. "How can we make sure World War I isn't forgotten."

Buckles asked his daughter, Susannah Flanagan, about progress toward a national memorial every week, sometimes daily.

"He was sad it's not completed," DeJonge said. "It's a simple straightforward thing to do, to honor Americans."

When asked in February 2008 how it felt to be the last survivor, Buckles said simply, "I realized that somebody had to be, and it was me."

Only two known World War I veterans remain, according to the Order of the First World War, a Florida group whose members are descendants of WWI veterans and include Buckles' daughter.

The survivors are Florence Green in Britain and Claude Choules in Australia, said Robert Carroon, the group's senior vice commander. Choules, who served in Britain's Royal Navy, was born in that country but now lives in Australia. Green turned 110 on Feb. 19, and Choules turns 110 in March, Carroon said.

Born in Missouri in 1901 and raised in Oklahoma, Buckles visited a string of military recruiters after the United States in April 1917 entered what was called "the war to end all wars." He was repeatedly rejected before convincing an Army captain he was 18.

More than 4.7 million people joined the U.S. military from 1917-18. By 2007, only three survived. Buckles went to Washington that year to serve as grand marshal of the national Memorial Day parade.

Unlike Buckles, the other two survivors were still in basic training in the United States when the war ended, and they did not make it overseas. When they died in late 2007 and 2008, Buckles became the last so-called doughboy -- and a soft-spoken celebrity.

He got fan mail almost every day, DeJonge said, and had enough birthday cards to fill several bushel baskets.

DeJonge had visited Buckles late last week and was driving back to Michigan with about 5,000 letters to organize and answer when he got the call telling him his friend had died.

"The letters are so heartfelt," he said. "Each night, Susannah would go in and sit at Papa's bedside and read them to Frank. That kept him going."

Buckles had been battling colds and other minor ailments this winter, but he was not ill at the time of his death.

The day before he died was warm, DeJonge said, and he spent three hours sitting in the sunshine on the porch of his farmhouse, talking with his daughter.

She worked diligently to keep Buckles in his own home, even though it exhausted his life savings. DeJonge said home health nurses and other medical care cost about $120,000 a year.

Details for services and arrangements will be announced later this week, but the family is planning a burial in Arlington National Cemetery. In 2008, friends persuaded the federal government to make an exception to its rules for who can be interred there.

Buckles had already been eligible to have his cremated remains housed at the cemetery. Burial, however, normally requires meeting several criteria, including earning one of five medals, such as a Purple Heart.

Buckles never saw combat but once joked, "Didn't I make every effort?"

U.S. Rep. Shelley Moore Capito and the rest of West Virginia's congressional delegation were also working Monday on a plan to allow Buckles to lie in repose in the rotunda of the U.S. Capitol.

According to the Architect of the Capitol's website, the last person to do so was President Gerald Ford.

The honor is reserved mostly for elected and military officials, but others have included civil rights activist Rosa Parks and unknown soldiers from both World Wars and the Korean War.

Sen. Jay Rockefeller called Buckles "a wonderfully plainspoken man and an icon for the World War I generation" and said he will continue fighting for the memorial Buckles wanted.

"He lived a long and rich life as a true American patriot," said Sen. Joe Manchin, "and I hope that his family's loss is lightened with the knowledge that he was loved and will be missed by so many."

Capito said Buckles "represented the very best of this great country-service, determination and patriotism."

The family asked that donations be made to the National World War One Legacy Project. The project is managed by the nonprofit Survivor Quest and will educate students about Buckles and WWI through a documentary and traveling educational exhibition.

"We have lost a living link to an important era in our nation's history," said Secretary of Veterans Affairs Eric Shinseki. "But we have also lost a man of quiet dignity, who dedicated his final years to ensuring the sacrifices of his fellow 'Doughboys' are appropriately commemorated."

In spring 2007, Buckles told The Associated Press of the trouble he went through to get into the military.

"I went to the state fair up in Wichita, Kansas, and while there, went to the recruiting station for the Marine Corps," he said. "The nice Marine sergeant said I was too young when I gave my age as 18, said I had to be 21."

Buckles returned a week later.

"I went back to the recruiting sergeant, and this time I was 21," he said with a grin. "I passed the inspection ... but he told me I just wasn't heavy enough."

Then he tried the Navy, whose recruiter told Buckles he was flat-footed.

Buckles wouldn't quit. In Oklahoma City, an Army captain demanded a birth certificate.

"I told him birth certificates were not made in Missouri when I was born, that the record was in a family Bible. I said, 'You don't want me to bring the family Bible down, do you?'" Buckles said with a laugh. "He said, 'OK, we'll take you.'"

Buckles served in England and France, working mainly as a driver and a warehouse clerk. An eager student of culture and language, he used his off-duty hours to learn German, visit cathedrals, museums and tombs, and bicycle in the French countryside.

After Armistice Day, Buckles helped return prisoners of war to Germany. He returned to the United States in January 1920.

After the war, he returned to Oklahoma, then moved to Canada, where he worked a series of jobs before heading for New York City. There, he landed jobs in banking and advertising.

But it was the shipping industry that suited him best, and he worked around the world for the White Star Line Steamship Co. and W.R. Grace & Co.

In 1941, while on business in the Philippines, Buckles was captured by the Japanese. He spent more than three years in prison camps.

"I was never actually looking for adventure," he once said. "It just came to me."