Wop May, Vic Horner, and the Nineteen Twenty-Nine Open-Cockpit Mercy Flight That Carried Diphtheria Serum Six Hundred Miles Into the Alberta Cold

In early January 1929, bush pilots Wop May and Vic Horner flew a fragile open-cockpit biplane roughly 600 miles from Edmonton into the far north of Alberta to deliver diphtheria antitoxin to a settlement facing an epidemic. They flew in temperatures near 40 below zero with no cabin heat, no navigation aids, and a smoldering charcoal heater in the cockpit to keep the serum from freezing. Their flight saved the community of Little Red River and helped transform how Canadians understood the airplane’s purpose.

What Was the 1929 Mercy Flight?

The mercy flight was an emergency mission to carry diphtheria serum from Edmonton to the isolated northern settlements around Little Red River and Fort Vermilion, Alberta. It was flown by pilot Wilfrid “Wop” May and mechanic-pilot Vic Horner in a light British biplane, the Avro Avian.

In the last days of December 1928, a man at Little Red River fell ill. The regional physician, Dr. Harold Hamman, recognized the symptoms immediately: diphtheria, a disease that grows a thick grey membrane across the throat until the airway closes. It was once so lethal to the young that it earned a grim nickname - “the strangling angel of children.”

Diphtheria spreads. With a mission, a Hudson’s Bay Company trading post, and families of trappers and Indigenous residents in the area, Dr. Hamman knew a single case could become an epidemic that wiped out the entire settlement before spring. He had a small amount of antitoxin on hand and used it, but he needed far more - and the nearest supply was 600 miles south in Edmonton.

Why Couldn’t the Serum Go by Land?

In the dead of a northern winter, there were no meaningful roads. Freight moved by dog team and horse-drawn sleigh over frozen rivers and bush trails. By that route, the doctor calculated the serum would take about two weeks to arrive.

The settlement would not survive two weeks. Word was relayed south by dog sled and telegraph until it reached the Deputy Minister of Health for Alberta, who faced a choice no one had really made before: send the serum the slow, safe way and hope - or put it in an airplane.

Why Was Flying So Dangerous in 1929?

In 1929, essentially no one flew the northern Alberta bush in winter. Bush flying in Canada was still being invented, mostly as a summer activity when floatplanes could land on lakes. In winter, engines wouldn’t start, the oil turned to tar, and there were no heated hangars, no reliable weather reports, and no navigation aids. Pilots navigated by following the bends of rivers from the open air.

The only aircraft available in Edmonton for the attempt was a little Avro Avian - a British-built light biplane meant as a trainer and sport plane. It was fabric over a wood-and-metal frame, powered by a small Cirrus engine of roughly 80–90 horsepower, with two open cockpits and no heat of any kind. It was, in every sense, a fair-weather airplane being asked to cross the coldest part of the Canadian winter.

Who Was Wop May?

The pilot, Wilfrid “Wop” May, carried a remarkable history. He earned the nickname “Wop” as a baby from a young cousin who couldn’t pronounce his name, and it stuck for life.

During the First World War, May was a green fighter pilot on one of his first combat flights when a red triplane latched onto his tail and chased him low across the ground. That triplane belonged to Manfred von Richthofen - the Red Baron - the deadliest ace of the war with 80 victories. May was nearly his 81st.

A fellow Canadian, Roy Brown, dove in to help, and in the chase that followed the Red Baron was shot down and killed. Historians still debate whether Brown’s guns or ground fire brought him down - but the pilot in the Red Baron’s sights in his final minute was Wop May. A decade later, May was running a small aviation company in Edmonton, and when the call came, he did not hesitate. His companion, Vic Horner, came along because no one flew that country alone in winter - a second pilot could nurse the engine and, if they went down, help them survive.

How Did They Keep the Serum From Freezing?

Diphtheria antitoxin is ruined if it freezes. To protect the glass bottles, the crew wrapped them in blankets and packed a small charcoal heater in with the cargo to hold it above freezing.

The solution nearly killed them. It meant flying an open-cockpit, fabric-covered airplane full of gasoline with a small fire smoldering aboard - and the heater gave off fumes, most likely carbon monoxide, that drifted into cockpits the crew couldn’t seal, because the entire airplane was effectively open to the air.

What Happened During the Flight?

May and Horner took off from Edmonton on January 2, 1929, and the cold hit immediately. Wind poured over the cowling at 80–90 miles per hour at sub-zero temperatures, straight into their faces for hours. Their goggles iced over from the inside and their breath froze on the fur around their mouths.

May later said the cold went so deep he lost feeling in his hands and feet and worked the controls almost from memory. They followed the rivers north - the Athabasca and the Lesser Slave - and landed at McLennan to warm up and refuel, barely able to climb from the aircraft.

Then the weather turned. A deeper arctic cold snap dropped down from the north, and the hardest leg still lay ahead: from McLennan to Fort Vermilion and Little Red River there was no settlement and nowhere to land and get warm. If the engine quit over that frozen bush, no one would find them until spring. They chose to press on, because children were dying and every hour mattered.

The little Cirrus engine never missed a beat. They kept it alive with old bush-flying craft - draining the oil at each stop, warming it by fire, and pouring it back in hot before starting. They reached Fort Vermilion, delivered the first serum to the doctor, then pushed on to cover more country as the outbreak spread. Then they turned around and flew all the way back - another 600 cold, fume-choked miles with no glory in it, only the hope the engine would hold.

What Happened When They Returned?

May and Horner reached Edmonton on January 6, 1929. By then the mercy flight was national news, carried across Canada by telegraph, radio, and newspaper. Thousands of people - some accounts say 5,000 to 10,000 - stood out on the frozen airfield in the January cold to greet them.

Both men were so frozen and sickened by the fumes that they had to be lifted from the aircraft. But the mission was done. The outbreak was stopped, and the settlement lived.

Why the Mercy Flight Mattered

Before this flight, most people saw the airplane as a toy - a plaything for barnstormers, record chasers, and wealthy hobbyists, not something that touched ordinary life. The mercy flight changed that overnight. A nation read over breakfast how a little biplane had reached a place nothing else could reach, beaten the distance and the season, and saved a town full of children.

That shift helped launch one of the world’s great bush flying traditions. The idea of the mercy flight and the airplane as a lifeline to remote country traces directly back to May, Horner, and that charcoal heater in an open cockpit.

Wop May kept flying, becoming a pioneer of northern Canadian aviation. He later helped direct a famous aerial manhunt across the Arctic and trained pilots in the Second World War. But of all his exploits - the dogfight, the records, the manhunt - this cold, dangerous slog to carry medicine to strangers may well have been his finest hour. It showed, plainly, what an airplane is truly for.

Key Takeaways

• Wop May and Vic Horner flew roughly 600 miles each way from Edmonton to northern Alberta in an open-cockpit Avro Avian to deliver diphtheria antitoxin in January 1929.
• They departed Edmonton on January 2 and returned on January 6, 1929, flying in temperatures near 40 below with no cabin heat and a charcoal heater protecting the serum.
• The pilot, Wop May, was the same rookie the Red Baron was chasing when the famous ace was killed in 1918.
• The flight halted a diphtheria outbreak - “the strangling angel” - and saved the settlement around Little Red River and Fort Vermilion.
• The mission reshaped public perception of aviation and helped establish Canada’s tradition of bush flying and life-saving mercy flights.