He went to war as a teenager, helped keep flimsy aircraft flying, survived his wounds and came home from World War I to a long - very long - and fruitful life.
But only in his last years did he discover his true mission: to remind new generations of the sacrifices of the millions slaughtered in the trenches, killed in the air, or lost at sea in what Britons call the Great War.
Allingham, who was the world's oldest man when he died Saturday at 113, attributed his remarkable longevity to "cigarettes, whisky and wild, wild women."
Jokes aside, he was a modest man who served as Britain's conscience, reminding young people time and time again about the true cost of war.
"I want everyone to know," he told The Associated Press during an interview in November. "They died for us."
He was the last surviving original member of the Royal Air Force, which was formed in 1918. He made it a personal crusade to talk about a conflict that wiped out much of a generation. Though nearly blind, he would take the outstretched hands of visitors in both of his, gaze into the eyes of children, veterans and journalists and deliver a message he wanted them all to remember about those left on the battlefield.
"I don't want to see them forgotten," he would say quietly. "We were pals."
Only a handful of World War I veterans remain of the estimated 68 million mobilized. There are no French veterans left alive; just one left now in Britain; and the last living American-born veteran is Frank Woodruff Buckles of Charles Town, West Virginia. The man believed to have been Germany's last surviving soldier has also died.
"It's the end of a era a very special and unique generation," said Allingham's friend, Dennis Goodwin. "The British people owe them a great deal of gratitude."
Born June 6, 1896, during the reign of Queen Victoria, Allingham would later recall sitting on his grandfather's shoulders waving a flag for King Edward VII's coronation in 1902. Transportation was horse drawn, coal was the primary fuel, street lighting was gas and in the financial heart of London, there was same-day mail delivery.
But the world was changing fast. In 1903, Wilbur and Orville Wright flew an airplane at Kitty Hawk, North Carolina, and in 1913, Henry Ford began making Model Ts on an assembly line in Michigan.
Allingham left school at 15 and was working in a car factory in east London when war broke out in 1914.
He spent the war's first months refitting trucks for military use, but when his mother died in June 1915, he decided to join up after seeing a plane circling a reservoir in Essex, east of London.
"It was a captivating sight," he wrote in his memoir. "Fascinated, I sat down on the grass verge to watch the aircraft. I decided that was for me."
That chance encounter with an early flying machine was to change his life.
It was only a dozen years after the Wright brothers first put up their plane, and Britain's air resources were primitive. Allingham and other valiant airmen set out from eastern England on motorized kites made with wood, linen and wire. They piled on clothes and smeared their faces in Vaseline, whale oil or engine grease to try to block the cold.
"To be honest, all the planes were so flimsy and unpredictable
as well as incapable of carrying large fuel loads - at the start of the war that both British and German pilots would immediately turn back rather than face each other in the skies if they did not enjoy height supremacy," Allingham would later write. "But I remember getting back on the ground and just itching to take off again."
As a mechanic, Allingham's job was to maintain the rickety craft. He also flew as an observer on a biplane. At first, his weaponry consisted of a standard issue Lee Enfield .303 rifle - sometimes two. Parachutes weren't issued.
He fought in the Battle of Jutland, the largest naval battle of World War I. He served on the Western Front, by now armed with a machine gun. He was wounded in the arm by shrapnel during an attack on an aircraft depot, but survived.
After the war he worked at the Ford motor factory and raised two children with his wife, Dorothy. She died in 1970, and when his daughter Jean died in 2001, friends say he waited to die, too. His will to live was waning; his life seemed without a larger purpose.
That's about the time he met Goodwin, a nursing home inspector who realized that veterans of Allingham's generation were not getting the care they needed to address the trauma they had experienced at the Somme, Gallipoli and Ypres and the other blood-drenched World War I battlefields. Some veterans ached to return to the battlefields to pay their respects to their slain friends, and Goodwin found himself organizing trips to France for that purpose.
He encouraged Allingham to share his experiences and the veteran, even though he had passed the century mark, started talking to reporters and school groups, providing the connection to a lost generation some had forgotten. He found himself leading military parades. He was made an Officer of France's Legion of Honor and received other honors.
He met Queen Elizabeth II and wrote his autobiography with help from Goodwin. It was called "Kitchener's Last Volunteer," a reference to Britain's Minister for War who rallied men to the cause. Prince Charles wrote the introduction.
He grew accustomed to being one of the last ones standing. Last year, he joined Harry Patch, Britain's last surviving World War I soldier, and the late Bill Stone, the country's last sailor, in a ceremony at the Cenotaph war memorial near the houses of Parliament in London, to mark the 90th anniversary of the war's end at the 11th hour of the 11th day of the 11th month in 1918.
As the wreaths were being laid, Allingham pushed himself up out of his wheelchair to place his arrangement at the base of the memorial - refusing the help of an officer deployed at his side. He leaned forward and placed the red poppy wreath beside the others. Tears flowed.
Allingham remained outspoken until his death, pleading for peace and begging anyone who would listen to remember those who died.
"I think we need to make people aware that a few men gave all they had to give so that you could have a better world to live in," he said. "We have to pray it never happens again."
Goodwin said Allingham's funeral will take place in Brighton. He is survived by five grandchildren, 12 great-grandchildren, 14 great-great grandchildren and one great-great-great grandchild.