Convoy SC-121

Convoy SC 121
Part of Battle of the Atlantic
A depth charge being loaded onto a depth-charge thrower aboard the corvette HMS Dianthus
Date 6–10 March 1943 Location North Atlantic Result German tactical victory
Belligerents
United Kingdom  United States  Canada	Germany
Commanders and leaders
Capt. H.C. Birnie RNR Capt. P.R. Heineman USN	Admiral Karl Dönitz
Strength
69 freighters 2 destroyers 3 cutters 4 corvettes	27 submarines
Casualties and losses
12 freighters sunk (55,673 GRT) 270 killed/drowned

Convoy SC-121 was the 121st 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 23 February 1943; and were met by the Mid-Ocean Escort Force Group A-3 consisting of the United States Coast Guard (USCG) Treasury-class cutter USCGC Spencer, the American Wickes-class destroyer USS Greer, the British and Canadian Flower-class corvettes HMS Dianthus, HMCS Rosthern, HMCS Trillium and HMCS Dauphin and the convoy rescue ship Melrose Abbey. Three of the escorts had defective sonar and three had unserviceable radar.

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 find convoys with the advantage of intelligence gained through B-Dienst decryption of British Naval Cypher Number 3. Only 20 percent of the 180 trans-Atlantic convoys, from the end of July 1942 until the end of April 1943, lost ships to U-boat attack.

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