Convoy SL 139 / MKS 30 Convoys SL 139 / MKS 30 were two Allied convoys which ran during the Battle of the Atlantic in World War II . SL 139 was part of the OS / SL series , between Britain and the South Atlantic , and MKS 30 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 November 1943 . They were the subject of a major 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 . German U - boat Control ( BdU ) had established a patrol line off the coast of Portugal , which had already attacked Allied convoys in October , leading to an inconclusive clash over Convoy SL 138 / MKS 28 . In order to maximize the protection for convoys on this route the Admiralty ahd begun to run these in tandem , bringing together the South Atlantic and the Mediterranean routes at Gibraltar . Protagonists . SL 139 left Freetown on 2 November 1943 , arriving off Gibraltar on 16 November . It comprised 42 ships and was escorted by an Escort Group , of nine warships . MKS 30 sailed from Port Said on 2 November , similarly arriving off Gibraltar on 16 November to meet SL 139 . The combined body of 66 ships then sailed for Britain . It was escorted by 40 Escort Group , of seven warships , led by HMS " Exe " ( Cdr . JS Dalison ) . The " Schill " patrol group , which had been active in this area since October , was now organized into three patrol lines west of Portugal , while aircraft of the " Luftwaffe " from searched the ocean for any sign of the approaching convoys . The first , " Schill 1 " , of seven U - boats , was the southernmost rake , running in a line to the west of Lisbon . The second , " Schill 2 " , of ten U - boats , was aligned west of Cape Finisterre in Spain , while the third , " Schill 3 " , of twelve U - boats , was 150 miles north of this , roughly along the 45 parallel . Action . The two convoys made their rendezvous on noon on 16 November 1943 , a total of 66 ships initially escorted by 40 EG , seven warships led by " Exe " . The combined convoys were sighted by German aircraft on late afternoon of 16 November , southwest of Cape St Vincent , but were able to evade the shadow during the night . On 18 November the convoys encountered " Schill 1 " ’ s patrol line . They were sighted by " U - 262 " , which was joined by two other boats ( " U - 333 " , " U - 515 " ) for the first assault . Also on the 18th the escort force was joined by 7 EG , a Support Group of five warships led by HMS " Pheasant " , ( Cdr LF Durnford - Slater ) . Meanwhile , further north , " U - 211 " of " Schill 2 " was caught by an RAF Wellington . She was depth - charged and sunk . , During the night of 18 / 19 November , in a series of forays the U - boats tried to penetrate the escort screen , but without success . " U - 333 " was attacked by " Exe " ; she was damaged when she was rammed by " Exe " and was forced to return to base . Meanwhile " U - 515 " had attacked and damaged the sloop " Chanticleer " ; she was forced to drop out , to be towed to the Allied Base in the Azores . " Chanticleer " survived the . . day journey , and was beached , but was declared unrecoverable . " U - 515 " was counter - attacked , and also forced to retire with damage , leaving " U - 262 " to shadow until " Schill 2 " could engage . On 19 November the convoys joined by 5 EG , a Canadian group of six warships led by " Nene " ( Cdr JD Birch ) operating in a Support Group role . Later on the 19th the convoys were also joined by destroyers " Winchelsea " and " Wrestler " , bringing the total escort strength up to nineteen warships . At dusk on 19 November the convoys encountered " Schill 2 " , which commenced an assault throughout the night of 19 / 20 November . Again , they were unable to penetrate the escort screen and during the night " U - 536 " was destroyed by " Nene " and " Snowberry " , Canada ’ s first Support group success . On 20 November the boats of " Schill 2 " remained in contact . They were reduced to a shadowing role and came under air attack attack by patrolling aircraft , but in a series of gun duels two aircraft were shot down , a Liberator of 53 Sqdn by " U - 648 " and an RCAF Sunderland of 422 Sqdn by " U - 618 " . None of the U - boats were lost or damaged by air attack , but " U - 538 " was caught by " Foley " and " Crane " and destroyed . , That night 20 / 21 November the convoy and pursuing U - boats reached the boats of " Schill 3 " which joined the fray . Again all attacks were unsuccessful , though no U boats were destroyed . On 21 November the convoy was joined by another Support group , 4 EG , comprising six warships led by " Bentinck " ( Cdr EH Chavasse ) , and by " Prince Robert " an RCN Armed Merchant Cruiser , fitted out as an AA gunship . During 21 November BdU called off the U - boat assault , but the convoy was now in range of strike aircraft based in Occupied France . On the afternoon of 21 November the " Luftwaffe " launched an attack using its new weapon , the He 293 guided missile . Twenty - five He 177 ’ s each carrying two He 293s took off to attack SL 139 / MKS 30 . At a distance of miles the drones were released , to be guided by radio control to their target . Despite AA fire from the escorts , particularly " Prince Robert " , two sips were hit . One , " Marsa " was sunk , and the other , " Delius " , was damaged . During this assault two aircraft were forced to return with mechanical trouble , and three others failed to return . Thi was the only attempt on the convoy by the " Luftwaffe " ; the convoy continued its voyage without further incident , docking at Liverpool on 26 November 1943 . Aftermath . Despite the concentration of U boats for this attack , the U - boat Arm failed to make any impact on the convoy . No merchant ships were sunk by the U - boats , though one escort was damaged and subsequently writtemn off , while three U - boats were destroyed . The " Luftwaffe " similarly had a disappointing result . Despite their new weapon , of which great things were expected , they saw only ship sunk and one damaged , for the loss of three aircraft . For the Allies , their confidence in their ability to protect convoys and destroy attacking U - boats continued , and this was further vindication of the Support Group policy , with no less than three Support Groups able to throw their weight into the conflict .