Capt. Roy Brown had ordered the young airman not to engage the enemy, but Lt. Wilfrid "Wop" May — a school chum from Edmonton — couldn't help himself.
It was April 21, 1918 — a century ago this Saturday — and the two Canadians in their canvas-covered Sopwith Camel biplanes were about to match wits with the deadliest ace of the First World War, Manfred von Richthofen, better known as the Red Baron.
As the engines of primitive German and British warplanes snarled in the skies over the Somme River in northern France, May joined the fight, only to have his guns jam as Richthofen's all-red Fokker triplane closed in from behind for what would have been his 81st kill.
"Brown saw that his buddy was in trouble," says Don Brodeur, Brown's grandson and a retired Royal Canadian Air Force pilot with more than 6,000 hours of flight time in fighter jets.
"Richthofen broke some of his own cardinal rules ... He followed May for too long, which is why Brown got on top of him."
As May flew fast and low over the French countryside, skimming over the scars left by trenches and bomb craters, Brown pitched his plane into a dive and aimed his machine-guns at Richthofen, firing bursts at long range.
"(Brown) wound that Camel up to 190 miles an hour, which was no mean feat," says David Bashow, editor of the Canadian Military Journal and a retired lieutenant-colonel who served 36 years with the RCAF.
"That aircraft was particularly unstable at high speeds."
What happened next has long been the subject of an intense debate, even as the world marks the 100th anniversary of the storied dogfight.
May escaped as Richthofen broke off to the right to avoid Brown's blasts and rising terrain, but that manoeuvre brought him within range of Australian Corps machine-guns on the ground.
Soon after Brown fired on the scarlet fighter aircraft, Richthofen crashed in a sugar-beet field, where he died from a gunshot wound to the chest. He was 25.
The Royal Air Force credited the 24-year-old Canadian, originally from Carleton Place, Ont., with the combat victory — his 10th.
However, the results from autopsies performed on Richthofen's body raised questions about who fired the fatal shot.
Over the years, some historians and forensics experts have suggested the orientation of Richthofen's wounds indicated the .303-calibre bullet must have been fired from the ground and not from Brown's guns, which fired the same type of ammunition.
"Over time, the Australians made a very compelling case for one of their troops on the ground," says Bashow, an associate professor at the Royal Military College of Canada in Kingston, Ont., and a former fighter pilot who logged 2,400 hours in the supersonic CF-104 Starfighter.
"(Brown's) flight-path geometry just does not work."
However, Brown's grandson disagrees, saying the more plausible explanation is that Brown fired a lucky shot.
"There is only one record," Brodeur said in an interview from his home in Victoria. "Both Canada and the U.K. attribute the shooting down of the Red Baron to Capt. A. Roy Brown. That's a fact to this day."
As well, Brodeur says his interpretation of what happened — as seen through the eyes of an experienced fighter pilot — has led him to conclude Richthofen's aircraft would have been practically inverted for the Australian theory to make sense.
"In movies, you see aircraft rolling in a dogfight, but it's a waste of time," says Brodeur, who flew several types of jet fighters and was a member of the Canadian Forces Snowbirds aerobatic squadron.
"It looks good in Hollywood films, but it's not something you do in an air-to-air fight."
Rob Probert, president of the Roy Brown Historical Society in Carleton Place, says there was nothing to be learned by examining Richthofen's downed plane because it had been damaged by artillery shells and quickly stripped by souvenir hunters.
"Brown was officially credited with the kill, and 100 years later that still stands," Probert says.
"The problem here in Canada is that there hasn't been a group championing Roy Brown's story, until our group came along. We're just trying to make sure the story doesn't get lost over time ... It's part of the Canadian psyche not to brag about our heroes."
Appropriately, the society will gather Saturday in Carleton Place, to fete the man they say brought down the Red Baron.
Regardless of who fired the fatal shot, one thing is for certain: Were it not for Brown's superior skills as a pilot and leader, one of the most celebrated aerial battles of the war would never have happened.
"I think he was a hero for sure — he never lost a man under his command," says Probert, who is part of a local effort to have a statue of Brown installed across from town hall in Carleton Place.
"It can't be refuted that Brown caused this battle to happen."
After the dogfight, Brown went to a nearby aircraft hangar to see Richthofen's body.
"His face, particularly peaceful, had an expression of gentleness and goodness, of refinement," Brown later wrote.
"Suddenly I felt miserable, desperately unhappy, as if I had committed an injustice. With a feeling of shame, a kind of anger against myself ... I could no longer look him in the face. I went away. I did not feel like a victor ... If he had been my dearest friend, I could not have felt greater sorrow."
Brown, who was in poor health and complained of being on the verge of a nervous breakdown, was later transferred to a flight training unit. He was badly injured in a crash on July 5, 1918, when his engine quit soon after takeoff.
Unlike Richthofen, whose martyrdom continues to be commemorated in books, movies and, of course, the perennial Peanuts cartoon, Brown's legacy is largely muted in Canada.
"He didn't really speak about his exploits," says Tim Cook, First World War historian at the Canadian War Museum in Ottawa.
"We don't have a whole lot of military heroes from the past who still resonate today. It has something to do with our national character. It has something to do with how we view war and peace. And, perhaps, there's the sense that Canadians are not always the best at backslapping and elevating their heroes."
Brown moved to Stouffville, Ont., after the war. He died of a heart attack in 1944 at the age of 50.
He is buried in Toronto, but his grave remained unmarked until a few years ago.
Michael MacDonald, The Canadian Press