Convoy SL 140 / MKS 31 Convoys SL 140 / MKS 31 were two Allied convoys which ran during the Battle of the Atlantic in World War II . SL 140 was part of the OS / SL series , between Britain and the South Atlantic , MKS 31 was one of the KMS / MKS series between Britain and the Mediterranean . They were sailing together on the Gibraltar homeward route , having made a rendezvous off Gibraltar in late November 1943 . They were the subject of a U - boat attack , as part of the German Navy ’ s ( " Kriegsmarine " ( KM ) ’ s ) renewed Autumn offensive . Background . Following the renewal of the U - boat offensive in the Atlantic , convoys on the UK / Gibraltar routes had again come under attack , leading to clashes over Convoy SL 138 / MKS 28 and Convoy SL 139 / MKS 30 . German U - boat Control ( BdU ) had subsequently re - organized its patrol lines off the coast of Portugal , so as to find and attack the next convoys on this route . As before , the Admiralty were running these in tandem , bringing together the South Atlantic and the Mediterranean routes at Gibraltar . Protagonists . SL 140 left Freetown on 12 November 1943 , arriving off Gibraltar on 24 November . It comprised 35 ships and was escorted by an Escort Group of four warships . MKS 31 sailed from Port Said on 13 November , similarly arriving off Gibraltar on 24 November to meet SL 140 . The combined body of 65 ships then sailed for Britain . It was escorted by B - 1 Escort Group , of seven warships , led by HMS " Hurricane " , ( Commander EC Bayldon ) . Opposing this force was patrol group " Weddigen " , consisting of thirteen U - boats , comprising boats already on station from the disbanded " Schill " group , with reinforcements from the North Atlantic and from bases in occupied France . Action . The two convoys made their rendezvous at noon on 24 November 1943 , a total of 65 ships initially escorted by the B - 1 Escort Group , of seven warships . The combined convoys were sighted by German aircraft in the late afternoon of 26 November , west of Cape St Vincent , but were able to evade the shadow with a radical course change during the night . The convoy was reinforced by the destroyer " Watchman " , also on the 26th . On 27 November the convoys were found again by aircraft , which brought in " U - 262 " . She commenced shadowing until other " Weddigen " boats could be homed - in . Also during the 27th the convoy was joined by 4 EG , a Support Group of five frigates led by HMS " Bentinck " ( Cdr EH Chavasse ) . By evening the U - boats had gathered and started their assault . Franke , in " U - 262 " was able to penetrate the escort screen into the convoy itself , he attacked the ships there from close range , a tactic used by aces Kretschmer and Schepke two to three years earlier . However his boldness was not rewarded by any success ; he fired at , and claimed hits on , three ships , but no hits were confirmed . The three other boats that penetrated the screen , " U - 764 " , " U - 107 " , and " U - 238 " , also failed to make any hits . During the night the convoy was again reinforced by the arrival of 2 EG , a Support Group led by Captain F . J . " Johnnie " Walker , Britain ' s most successful anti - submarine warfare commander , in HMS " Starling " . This brought the total number of escorts for the convoy to seventeen warships . On 28 November " U - 238 " picked up two allied airmen whose aircraft had crashed . U - 238 ’ s skipper , Horst Hepp , radioed a long account of his interrogation of them , which was intercepted and tracked by HF / DF ( radio direction finding ) . Hepp was meanwhile ordered to meet " U - 764 " , which was returning to base , in order to transfer the prisoners . Allied forces were sent to intercept the two U - boats , with a view to rescuing the airmen , and prevent the two boats from getting away . Both " U - 764 " and " U - 238 " were attacked the following day by aircraft from the escort carrier USS " Bogue " ; both were damaged , but both were able to escape . Also on 28 November , 2 EG located " U - 842 " and subjected her to a prolonged attack , but she also was able to escape . But by now outnumbered by the convoy escort , " Weddigen " had little chance of achieving any success ; BdU ordered a halt to the attack . SL 140 and MKS 31 continued their passage without further incident , arriving at Liverpool on 26 November 1943 . Aftermath . Despite the energy of the attack on SL 140 / MKS 31 no ships were sunk , nor U - boats destroyed . The escort had successfully beaten off every attack , although the failure to destroy any of the attacking U - boats , despite the presence of two Support Groups , was disappointing to the Allies . Franke , of " U - 262 " received the Knight ' s Cross of the Iron Cross for this and previous actions on this patrol ; significantly the citation commented on the toughness and tenacity shown as the reason for the award , rather than for any major success , as in previous years . BdU recognized that in this phase of the U - boat offensive " the prospects of sinkings were slight "