Convoy SC 107

Convoy SC 107 was the 107th of the numbered series of World War II slow convoys of merchant ships from Sydney, Cape Breton Island to Liverpool. The ships departed New York City on 24 October 1942 and were found and engaged by a wolfpack of U-boats which sank fifteen ships. It was the heaviest loss of ships from any trans-Atlantic convoy through the winter of 1942–43. The attack included one of the largest non-nuclear man-made explosions in history, when U-132 torpedoed ammunition ships SS Hobbema and SS Hatimura - both were sunk, one exploded, with the German submarine also being destroyed in the explosion.

Background

As western Atlantic coastal convoys brought an end to the "Second Happy Time", Admiral Karl Dönitz, the Befehlshaber der U-Boote (BdU) or commander in chief of U-Boats, shifted focus to the mid-Atlantic to avoid aircraft patrols. Although convoy routing was less predictable in the mid-ocean, Dönitz anticipated that the increased numbers of U-boats being produced would be able to effectively search for convoys with the advantage of intelligence gained through B-Dienst decryption of British Naval Cypher Number 3. However, only 20 percent of the 180 trans-Atlantic convoys sailing from the end of July 1942 until the end of April 1943 lost ships to U-boat attack.

Discovery

B-Dienst decrypted message traffic detailing routing and composition of convoy SC 107, and fifteen U-boats of wolfpack Veilchen (violet) were deployed to intercept it. The convoy was found and reported by U-522, patrolling the same general area as wolfpack Veilchen, on 29 October as the Western Local Escort Force turned the convoy over to Escort Group C-4, supported by the convoy rescue ship Stockport. River-class destroyer HMCS Restigouche obtained a HF/DF bearing when U-522 sent the first convoy contact report at 16:24, and the convoy made a course change after dark in the hope of evading the shadowing U-boat.