From 1942 to 1944, fifteen German submarines destroyed or severely damaged twenty-seven ships, including three Canadian warships, a U.S. Army troop transport, and the Newfoundland ferry " Caribou " . More than 250 lives were lost. It was the only battle of the twentieth century to take place within Canada s boundaries, and the only battle to be fought almost exclusively by Canadian forces under Canadian, rather than alliance, high command. And for more than forty years the battle was characterized as a Canadian defeat. But was it a defeat? Drawing on new material from wartime records including ultra-top-secret Allied decryptions of German naval radio communications, Roger Sarty shows that Canada mounted a successful defence with far fewer resources and in the face of much greater challenges than previously known. He draws vivid pictures of the intense combat on Canada s shores and the interplay of the St. Lawrence battle with war politics in Ottawa, Washington, and London. At the same time, he weaves a second story: how researchers reassembled the scattered war records in Canada, Britain, the United States, and Germany, and brought the long-forgotten battle to life for new generations of Canadians and international audiences. "