At about 4 a.m. on Dec. 1, 1940, three torpedoes streamed through the frigid North Atlantic.
Two missed their target, the destroyer HMCS Saguenay.
The third fired from the Italian submarine Argo hit with such force it lifted the ship's bow and threw Able Seaman George Borgal of Halifax, just 19 and keeping night watch on the open bridge, up into the air.
"I went flying," he told author Blake Heathcote years later for the book "Testaments of Honour: Personal Histories of Canada's War Veterans."
"My left leg was numb when I got up and I felt the ship start to roll, back and forth, and I thought she was going to go," he said. "Our mast was broken and a fire broke out and our bow was gone."
The Saguenay lost 21 men that night but managed to steam about 450 kilometres — backwards — into port at Barrow-in-Furness, England, for repairs.
She was among the hundreds of vessels that braved every kind of weather, from hurricane-force storms to giant seas, as they faced the constant underwater threat of enemy submarines during the Battle of the Atlantic.
Canada played a crucial, largely unsung role in the fight to maintain shipping supply lines to Great Britain, the vital Allied stronghold against German forces advancing across Europe.
The Battle of the Atlantic was the longest and arguably most important campaign of the Second World War. It stretched from the Sept. 3, 1939, sinking of the British passenger liner Athenia off the coast of Ireland until the last German U-boats surrendered after Victory in Europe Day in May 1945.
The United Kingdom relied on constant arrivals from North America of troops, food, fuel, steel, aluminum and everything else needed to power its war machine against the Nazis.
Air travel and transport was still limited, said Marc Milner, author of "Battle of the Atlantic" and director of the Gregg Centre for the Study of War and Society at University of New Brunswick.
"Britain is an arsenal of democracy but the stuff's got to get there by boat," he said in an interview. "The war cannot be won without winning the Battle of the Atlantic."
Keeping supply lines open to the United Kingdom laid the ground work for Normandy and other operations that ultimately sealed Allied victory, Milner said.
"The Battle of the Atlantic could not have been won without Canada's contribution," he added. "By the winter of 1942-43, fully half of all the escorts on the main routes between North America — New York and Halifax — and British ports are Canadian naval escorts."
The convoy system in which warships guarded supply-loaded merchant ships from submarine attack was "the bedrock of Allied victory," Milner said.
Canadians were the quiet administrators, the air traffic controllers of the sea, who kept a complex operation going for much of the conflict.
"Canada was a major player in naval control of shipping and naval intelligence in the Battle of the Atlantic," Milner said. "We actually ran all of that stuff for all of North America until about the middle of 1942 when the Americans were finally up to speed and were able to take over their own section of the North Atlantic."
"We're the people who trained them," as the U.S. entered the war after Japan bombed Pearl Harbour on Dec. 7, 1941.
The Royal Canadian Air Force also made up about one-third of all aircraft and crew protecting the convoys from above, Milner said.
Former British prime minister Winston Churchill would later write that the Battle of the Atlantic was so pivotal that all other war efforts by land or air depended on its outcome.
"The only thing that ever really frightened me during the war was the U-boat peril," he wrote in "Their Finest Hour," part of his six-volume history of the Second World War.
Shipping losses reached a startling peak in 1942, raising alarms that Britain might not be able to import the yearly requirement of 25 to 30 million tonnes of food, raw materials, oil and other goods, Milner said.
Canadians stepped up as support staff to keep goods flowing at a time when the Royal Canadian Navy was still a comparatively fledgling force, he said.
"We did a lot with armed yachts and old trawlers and anything that would go.
"It allowed the British in particular to get really good at what they were doing, which was killing submarines."
The Royal Canadian Navy grew in that period from 10 modern warships and 3,276 personnel to 400 warships and almost 100,000 members. By 1945, it was the world's fourth largest navy.
It was one motley crew in the war's earliest stages, Milner said. Canadian corvette commanders were often former reservists or merchant seamen called to service — including a fair number of ex-liquor movers.
"And then there were people from the marine service of the RCMP who'd spent much of the '30s chasing them while they were running rum around the East Coast.
"You had this curious navy made up of characters on both sides of the law who were then out fighting Germans."
Milner hails those Merchant Navy sailors as true heroes who, despite high casualty rates, had to fight decades after the war for official recognition and veteran benefits.
He also specially mentions the corvette commanders and merchant vessel captains who worked relentless schedules under punishing stress. Many senior officers did not survive long after the war, he said.
They were men like Chummy Prentice, captain of the corvette HMCS Chambly who helped log the Royal Canadian Navy's first sinking of a U-boat in September 1941.
Prentice sported a monocle and didn't bat an eye when his whole crew turned up one day with their own eye pieces, Milner said.
"It's said that Prentice threw his head back, flipped the monocle in the air, caught it between his eyelid and his cheek and said: 'When you can do that, you can all wear monocles.'"
George Borgal, the son and namesake of that young watchman who survived the 1940 torpedo attack on the Saguenay, also marvels at the endurance of those crews.
"He would have nightmares," he said of his father, who lived through other close calls at sea, including a ramming with another vessel and a hurricane.
"You have to admire the strength of character of people who go through that."
Borgal is now head of a working group with the Canadian Naval Memorial Trust aimed at building Battle of the Atlantic Place. It would be a new museum in Halifax showcasing HMCS Sackville — a surviving corvette — and Canada's role in the campaign.
"It was crucial to the success of land battles," Borgal said of the country's collective effort, ensuring more than 25,000 merchant vessels crossed the Atlantic under Royal Canadian Navy escort.
"Without the battle having been won, Normandy wouldn't have happened, the relief of Stalingrad wouldn't have happened and the course of our future would have looked very different."
Every year on the first Sunday of May, Canada's naval forces honour those lost at sea during the Second World War. They pause, pray and remember the legacy of the Battle of the Atlantic as they pledge themselves anew: "Ready, aye, ready."