Convoys ONS 18 / ON 202 ONS 18 and ON 202 were North Atlantic convoys of the ONS / ON series which ran during the battle of the Atlantic in World War II . They were the subject of a major U - boat attack in September 1943 , the first battle in the German Navy ' s ( " Kriegsmarine " / KM ' s ) autumn offensive , following the withdrawal from the North Atlantic route after Black May . Background . Following the defeats of May 1943 , and the devastating losses incurred by the U - boat Arm ( " U - Bootwaffe " , or UBW ) Adm Dönitz had withdrawn from attacks on the North Atlantic route while awaiting tactical and technical improvements . Chief among these was the T - 5 acoustic torpedo , with which ( it was planned ) the convoy escorts could be attacked and eliminated , leaving the merchant ships defenceless . By September 1943 these were ready , and U - boat Control ( " Befehlshaber der Unterseeboote " , BdU ) dispatched a patrol group of 21 boats , code - named " Leuthen " , to renew the attack on the North Atlantic route . Ships involved . In September 1943 BdU had established the patrol line " Leuthen " of 21 U - boats south of Greenland ; these were to intercept west - bound convoys as they were about to enter the Greenland Air Gap , where Allied aircraft were reckoned to be unable to operate due to the extreme range . " Leuthen " was to harry any convoy it encountered while crossing the gap , before breaking off to repeat the onslaught with the east - bound convoys . On 12 September 1943 convoy ONS 18 left Liverpool bound for Halifax . Composed of 27 ships it was protected by B - 3 Escort Group , comprising 2 destroyers , " Escapade " and " Keppel " , ( Cdr MB Evans RN , the Senior Officer : Escort ) ; the frigate " Towey " , and 5 corvettes ; " Narcissus " , " Orchis " , " Roselys " , " Lobelia " and " Renoncule " . ONS - 18 was also accompanied by the MAC carrier " Empire MacAlpine " . When Western Approaches Command became aware of " Leuthen " , it was decided to reinforce ONS 18 ; the following convoy , ON 202 was ordered to close up , and a support group , SG 9 , sent to join . ON 202 had left Liverpool on 15 September , composed of 38 ships and escorted by Canadian escort group C - 2 , comprising 2 destroyers , " Gatineau " ( commanded by Lt . Cdr PW Burnett RN , SOE ) and " Icarus " ; the frigate " Lagan " , and 3 corvettes ; " Drumheller " , " Kamloops " and " Polyanthus " . Support Group 9 comprised destroyer " St Croix " , frigate " Itchen " ( Cdr CE Bridgman RN , SOE ) and 3 corvettes , " Chambly " , " Morden " and " Sackville " . Altogether the 65 ships were escorted by 19 warships , to face an attack from 21 U - boats . Action . On 19 September ONS 18 was sighted by " U - 270 " ; after sending a sighting report she was authorized to attack . Closing in " U - 270 " fired a T - 5 acoustic torpedo at " Lagan " , damaging her stern , the first case of an Allied warship to be damaged by the new weapon . The escorts counter - attacked , but " U - 270 " escaped , though " Escapade " was damaged by a misfire from her Hedgehog . Both " Lagan " and " Escapade " were forced to detach , returning to base under escort . The " Leuthen " boats closed in during 19 September , but 2 were attacked by air patrols , which , since the introduction of a number of Very Long Range ( VLR ) Liberator s during the summer , had been extended into the Air Gap . " U - 341 " was attacked and sunk by a Liberator from 10 Squadron RCAF . " U - 338 " was attacked by a Liberator of 120 Sqdn RAF which was credited with the kill ; however post - war analysis showed that " U - 338 " was only damaged by this , though was later engaged and sunk by the corvette " Drumheller " of C 2 group . On the night of 19 / 20 several " Leuthen " boats were in contact ; " U - 260 " attacked , but gained no hits . " U - 238 " fired on 2 ships , sinking one , " Theodore Dwight Weld " , and damaging another , " Frederick Douglass " . She fell out of the convoy , and was sunk later in the day by " U - 645 " . On 20 / 21 a dozen boats were in contact , and 8 were able to attack . " U - 305 " hit " St Croix " , which sank with the loss of 66 of her crew . " U - 952 " hit " Polyanthus " , which exploded and sank , leaving 1 survivor . He , and 81 men from " St Croix " , were picked up by " Itchen " . " U - 386 " was damaged by depth - charge attack and was forced to retire ; " U - 603 " was ordered to rendezvous , but was thwarted by air attacks . " Leuthen " remained in contact , and on the night of 21 / 22 renewed the attack . " U - 377 " attacked , claiming hits , but these were not confirmed ; she was attacked and damaged by aircraft and retired . " U - 230 " attacked , but again no hits were confirmed , she also was attacked by an unidentified escort and forced to retire . " U - 229 " was attacked and destroyed , this being credited to " Keppel " , Evans ’ flagship . " U - 422 " was damaged by air attack , but was able to continue . On 23 September the convoys reached the Grand Banks area , where fog hindered visibility both of the air patrols and the attacking " Leuthen " boats . " U - 238 " was able to penetrate the escort screen and sank 3 ships ; " Skjelbred " , " Oregon Express " , and " Fort Jemseg " . " U - 666 " torpedoed " Itchen " ; she sank , leaving just 3 survivors from her own crew and those of " Polyanthus " and " St Croix " she was carrying . " U - 952 " sank " Steel Voyager " and damaged " James Gordon Bennett " . " U - 758 " attacked , but had no hits confirmed and was herself damaged by a depth - charge attack . Poor visibility , fuel shortages , and fatigue now beset both U - boats and escorts , but BdU , believing the attack to have been a great success , ordered " Leuthen " to break off the attack . Claims by the various boat amounted to 12 escorts and 9 ships sunk , and a further 2 ships damaged Actual losses were 3 escorts and 6 ships and 1 damaged and 1 damaged , while 3 U - boats were destroyed and a further 3 damaged , being forced to return to base . Both convoys continued to their destinations , ONS 18 reaching Halifax on 29 September , while ON 202 arrived at New York on 1 October . Conclusion . Believing the new tactics and weapons to be a great success , BdU continued the offensive . " Leuthen " was disbanded , with 12 boats forming a new patrol line , " Rossbach " , joined by 9 boats from home bases to attack the next set of east - bound convoys . The Admiralty were also encouraged by the result . Despite the losses , ( which were serious ) , 90 % of the ships had arrived safely . The losses , while serious , were no more grievous than during the battles of late 1942 and early 1943 . Thus they were confident the escorts would be able to meet the challenge of the U - boat Arm ' s new weapons and tactics . Tables . a ) Allied ships lost . b ) Allied warships lost . c ) Axis submarines lost