Convoy SC 7 SC - 7 was the code name for a large Allied World War II convoy of 35 merchant ships and six escorts which sailed eastbound from Sydney , Nova Scotia for Liverpool and other United Kingdom ports on 5 October 1940 . While crossing the Atlantic , the convoy was intercepted by one of the German Navy ' s submarine wolfpacks . During the ensuing battle , the escort was completely overwhelmed and 20 of the 35 cargo vessels were sunk and 2 more damaged , with 141 lives lost . The disastrous outcome of the convoy demonstrated the German submarines ' potential of being able to work more efficiently using wolf pack tactics and the inadequacy of British anti - submarine tactics at the time . Ships of the convoy . The slow convoy SC - 7 left Sydney , Nova Scotia on 5 October 1940 bound for Liverpool and other British ports . The convoy was supposed to make 8 knots , but a number of its 35 merchant ships were much slower than this . The convoy consisted of older , smaller ships , mostly with essential cargoes of bulk goods . Much of the freight on these ships originated on Canada ' s east coast , especially from points to the north and east of Sydney . Typical cargoes included pit props from eastern New Brunswick for the British coal mines , lumber , pulpwood , grain from the Great Lakes ports , steel and steel ingots from the Sydney plant , and iron ore from Newfoundland bound for the huge steel plants of Wales . The largest ship in the convoy was the 9 , 512 - ton oil tanker , belonging to the British Admiralty , which was bound for the Clyde with fuel for the Royal Navy . Another ship , the British , carried a valuable cargo of trucks . Many of the ships were British , but the convoy also included Greek , Swedish , Norwegian and Dutch vessels . The convoy commodore , Vice Admiral Lachlan Donald Ian Mackinnon , a retired naval officer who volunteered for this civilian duty , sailed in , a British ship of . As convoy commodore , Mackinnon was in charge of the good order of the merchant ships , but did not command the escort . The was sole naval escort for the first three quarters of the journey . There was no aircraft protection in 1940 for Allied ships in the Atlantic Ocean after leaving coastal regions . " Scarborough " would have had little chance against a surface attack by a German raider . Many of the merchant ship captains were resentful at having to sail in convoy , and would have preferred to take their chances on their own rather than risk such a slow crossing with a weak escort . They were often uncooperative ; at one point early in the voyage " Scarborough ' s " captain was shocked to find a Greek merchant ship in the convoy travelling at night with her lights on . The first attacks . The convoy sailed on Saturday 5 October 1940 . On the first day , one ship , the SS " Winona " dropped out with mechanical trouble , and had to return . As bad weather set in on the 11th , several ships became separated , and were forced to sail independently . One of these , the SS " Trevisa " , was a small Canadian Laker of 1 , 813 tons with a cargo of lumber destined for Scotland . She was sighted by " U - 124 " on the 16th and sunk . Another , the Greek freighter SS " Aenos " was seen by " U - 38 " , and sunk on 17th ; but SS " Eaglescliffe Hall " , another Laker , avoided this fate , and was able to rescue survivors from " Aenos " , before arriving safely at Rothesay on the 19th . A fourth straggler regained the convoy on the 15th . On the 17th as the convoy entered the Western Approaches " Scarborough " was joined by the sloop " Fowey " and the new corvette " Bluebell " . Later that day they were sighted by " U - 48 " , which attacked , sinking two ships including the tanker " Languedoc " . " Scarborough " counter - attacked , driving " U - 48 " deep so she was unable to shadow or report . However the attack was prolonged unwisely , and the convoy moved so far ahead " Scarborough " was unable to rejoin . On the 18th SC 7 was joined by the sloop " Leith " , and the corvette " Heartsease " , and " Leith " assumed command . Later that day " U - 38 " , sighted the convoy and attacked , damaging SS " Carsbreck " . " Leith " and " Heartsease " attacked without success , though " U - 38 " was driven off , and " Heartsease " was detailed to escort " Carsbreck " home , weakening the escort further . The night of the U - boats . On the night of 18th / 19th five boats made a concerted attack . They were " U - 46 " , " " " U - 99 " , " U - 100 " , " U - 101 " and " U - 123 " . " U - 99 " was captained by the famous ace " Korvettenkapitän " Otto Kretschmer . The attack was coordinated from Lorient by Admiral Karl Dönitz and his staff . An early casualty was the iron ore ship , SS " Creekirk " , bound for Cardiff , Wales . With her heavy cargo , she sank like a stone , taking all 36 crew members with her . Later that night , SC 7 lost many of its members , including the SS " Empire Brigade " with her cargo of trucks and six of her crew and the SS " Fiscus " with her cargo of steel ingots from Sydney . She sank like a stone as well , taking with her 38 of her 39 man crew . Also among the casualties was the commodore ' s ship , SS " Assyrian " , down with 17 crew ( though Commodore Mackinnon was rescued after a long immersion in the chilly waters ) . In all , 16 ships were lost in this six hour period . On 18 October , was torpedoed by " U - 101 " and was abandoned . She was torpedoed again on 19 October by " U - 100 " but remained afloat . She was towed to the Clyde and later repaired at Greenock . The escorts were unable to prevent any of these losses ; their responses were uncoordinated and ineffective . They never realised that the attacking submarines did not attack submerged or from outside the convoy , but were actually running surfaced between the ships inside the convoy . Therefore the escorts were unable to mount any serious attacks on the U - boats , and had to spend much of their time rescuing survivors . Aftermath . During the daytime of the 19th the escorts , loaded with survivors , gathered together those ships that remained . " Fowey " collected eight ships and made for the Clyde , arriving there a few days later . " Scarborough " passed through the scene of the battle later on the 19th ; she found wreckage , but no survivors . Later that afternoon " Leith " met " Heartsease " , still escorting the damaged " Carsbreck " ; together they headed for the Gourock , collecting two more stragglers on the way . " Bluebell " with over 200 survivors on board , headed directly for the Clyde , arriving on the 20th . SC 7 had lost 20 ships out of 35 , of which seven fell to Kretschmer ' s " U - 99 " . The total tonnage lost was . The blackest days . Meanwhile , the arrival of Convoy HX - 79 in the vicinity had diverted the U - boat s and they went on to sink 12 ships from HX - 79 that night . No U - boats were lost in either engagement . The loss of 28 ships in 48 hours made 18th and 19 October the worst two days for shipping losses in the entire Atlantic campaign . Conclusion . The attack on SC 7 was a vindication of the U - boat Arm ' s wolf - pack tactic , and was the most successful U - boat attack of the Atlantic campaign . By contrast the convoy escort was ineffective in guarding against the attack . Convoy tactics were rudimentary at this early stage of the war . The escorts ' responses were uncoordinated , as the ships were unused to working together with a common battle - plan . Command fell to the senior officer present , and could change as each new ship arrived . The escorts were torn between staying with the convoy , abandoning survivors in the water , as DEMS regulations demanded , and picking them up , leaving the convoy unprotected and risking being torpedoed themselves .