Between 1942 and 1944, 23 ships were sunk by German submarines and hundreds of lives were lost.
Kapitänleutnant Karl Thurmann had dispatched five ships and damaged another during U-553’s first six missions in far-ranging patrols in the North Atlantic. His seventh mission brought him to Canadian waters.
In the late hours of May 11, 1942, off the Gaspé Peninsula, the SS Nicoya, a British vessel en route to join a convoy in Halifax, crossed his path. U-553 launched a torpedo. As the crew was abandoning the ship, a second torpedo sealed its fate, and that of six crew. The next morning, 111 survivors were rescued.
Two hours later, U-553 struck again, sinking the SS Leto; 12 of its 43 crew were killed.
The Royal Canadian Navy had expected attacks for some time, but it was pulled in many directions and had few resources patrolling areas not under threat of attack. U-553 changed that. Minesweepers and aircraft were dispatched from Nova Scotia, and marine traffic on the Saint Lawrence was shut down by the Navy’s Atlantic Coast Command.
Seven weeks later, a convoy of a dozen vessels heading from Quebec to Nova Scotia was attacked by a different submarine, and three ships were sunk near Rimouski.
Ships were diverted from the Atlantic for protection of Saint Lawrence vessels, and aircraft began hunting submarines in earnest.
Despite this, attacks continued over the summer and into the fall.
The deadliest attack occurred Oct. 14, when the ferry SS Caribou, with 237 passengers and crew aboard, was torpedoed by U-69. The ferry’s escort HMCS Grandmere tried to ram the sub and dropped depth charges, but the U-boat escaped. Only 103 ferry survivors were rescued.
It was decided to close the Saint Lawrence to overseas shipping, although it was still used by domestic vessels. Aerial and naval patrols were increased. Historians have determined the largest deployments of U-boats to the Saint Lawrence took place in the fall of 1942, but due to increased aerial and naval patrols, and their bombs and depth charges, submarines were forced to stay submerged much of the time.
The U-boats were persuaded to seek easier pickings.
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