Convoy ON 166 Convoy ON 166 was the 166th of the numbered ON series of merchant ship convoys Outbound from the British Isles to North America . Sixty - three ships departed Liverpool 11 February 1943 and were met the following day by Mid - Ocean Escort Force Group A - 3 consisting of the USCG Treasury Class Cutter s " Campbell " and " Spencer " and the Flower class corvette s " Dianthus " , " Chilliwack " , " Rosthern " , " Trillium " and " Dauphin " . 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 . 21 February . On 20 February " U - 604 " sighted the convoy scattered by sailing 8 days in a northwesterly gale . " U - 332 " torpedoed the straggling Norwegian " Stigstad " on the morning of 21 February . " U - 623 " was sunk by a No . 120 Squadron RAF B - 24 Liberator that afternoon , and " Campbell " attacked a U - boat that evening . Postwar analysis concluded that " Campbell " sank " U - 225 " , but more recent re - evaluation indicates the attack may have destroyed " U - 529 " . " U - 92 " torpedoed the British " Empire Trader " at 2032 and the Norwegian " NT Nielsen Alonso " at 0153 on the night of February 21 – 22 . Both ships were hit by a single torpedo on the port side , flooding the forward hold , and boiler room , respectively . " ORP Burza " from the following convoy ONS 167 was ordered to reinforce the convoy escort . 22 February . " U - 606 " torpedoed the British " Empire Redshank " and American " Chattanooga City " and " Expositor " after sunset 22 February , but was damaged by depth charge s from the recently arrived " Burza " . " Campbell " was disabled in a collision with " U - 606 " . Twelve men were rescued from the crew of the sinking U - boat . " Burza " left the convoy to tow " Campbell " back to port . The Convoy rescue ship " Stockport " was sunk by " U - 604 " while returning to the convoy after rescuing men from the three ships torpedoed by " U - 606 " . 23 February . " U - 628 " torpedoed thePanamanian " Winkler " at 0420 and Norwegian " Glittre " at 0425 . " U - 186 " torpedoed the American " Hastings " about 0430 and British " Eulima " at 0458 on 23 February . " Spencer " , " Rosthern " and " Chilliwack " remained with the convoy and " Dianthus " left to refuel . 24 February . " U - 600 " torpedoed the Norwegian " Ingria " at 0520 before dawn on 24 February . " U - 653 " torpedoed the straggling American Liberty ship " Jonathan Sturges " . 25 February . " U - 628 " hit the British " Manchester Merchant " with two torpedoes on the starboard side at 0527 before dawn 25 February . Aftermath . The U - boats discontinued the attack on 26 February . The surviving ships in the convoy were joined by from Halifax , Nova Scotia on 28 February with escorts , and . They reached New York City on 3 March 1943 .