'Markgraf' was a U-boat wolfpack operation in the Atlantic against the ON.10, ON.11 and SC.42 convoys (28 August/16 September 1941).

The U-boats of this wolfpack were U-38, U-43, U-81, U-82, U-84, U-85, U-105, U-202, U-207, U-432, U-433, U-501, U-569 and U-652, and for the loss of Oberleutnant Fritz Meyer’s U-207 and Korvettenkapitän Hugo Förster’s U-501 sank 17 ships (64,236 tons) and damaged four ships (14,132 tons).

On 1 September 'Ultra' decrypts of the radio messages sent by Vizeadmiral Karl Dönitz, the Befehlshaber der Unterseeboote, on 28, 30 and 31 August revealed much of the U-boat dispositions in the Atlantic, and the Allies therefore rerouted both the ON.10S and ON.11F westbound convoys and the HX.146 and SC.41 eastbound convoys to pass to the north of the locations of the 'Markgraf' wolfpack. At the same time a pair of small convoys (two ships bound from Reykjavik to Argentia and two ships bound from Argentia to Reykjavik) were also rerouted to clear the same wolfpack.

On 4 September a British aeroplane informed the US destroyer Greer, bound for Iceland, that there was a U-boat in its vicinity. The destroyer steamed to the location indicated and located the submerged U-boat. The British aeroplane depth-charged this boat, U-652, which believed that it was the neutral US destroyer which had delivered the attack, and tried to attack Greer. The destroyer evaded the attack and in turn depth-charged the U-boat, although without success.

On the same day the 'Markgraf' wolfpack was ordered to move 175 miles (280 km) farther to the west, just after the ONS.10S convoy, escorted by the US Task Unit 1.1.5 (destroyers Bernadou and Lea) had passed through the area. When this order was decrypted on 6 September, the HX.147 convoy and Lieutenant Commander John D. Connor’s US Task Unit 1.1.7 (destroyers Lansdale, Gleaves, Madison and Charles F. Hughes), supported by Lieutenant Commander S. W. Davis’s Canadian 20^th Escort Group (destroyer Columbia and corvettes Wetaskiwin, British Gladiolus and Free French Mimose), was rerouted to the north and just evaded the new patrol line.

On 5 September Förster’s U-501 sank the 2,000-ton Norwegian Einvik, a straggler from the SC.41 convoy. On 6 September, after waiting fruitlessly for sighting reports, Dönitz decided to spread the 'Markgraf' wolfpack over a larger area to the south-east of Greenland as a means of improving the possibility of convoy encounters. When this order was decrypted on 8 September the Allies had problems in exactly identifying the reference points, but attempts were nonetheless made to reroute convoys round the perceived danger area. Three convoys, namely ON.12S, HX.148 supported by the British 22^nd Escort Group (destroyer Richmond and corvettes Candytuft, Bittersweet and Fennel) and SC.43 supported by Commander P. J. Fitzgerald’s British 18^th Escort Group (destroyers Churchill and Chesterfield, and corvettes Arrowhead, Camellia, Eyebright and Celandine), had to make a wide detour to the south, as did the US Task Force 15 (battleship Idaho, heavy cruisers Tuscaloosa and Vincennes, and destroyers Winslow, Sampson, Anderson, Mustin, O’Brien, Walke, Morris, Benson, Niblack, H. P. Jones, MacLeish, Truxtun, Overton, Reuben James and Bainbridge), which was escorting nine transports with a US Army brigade to relieve the US Marine force on Iceland in 'Indigo III'. The escorting destroyers attacked eight different assumed U-boat contacts, but none of these was real.

The SC.42 convoy of 64 ships, support by Lieutenant Commander J. C. Hibbard’s Canadian 24^th Escort Group (destroyer Skeena and corvettes Alberni, Kenogami and Orillia) could not haul round to the south in the severe storm that was hitting the convoy, and was ordered to move closer to the Greenland ice barrier. Early on 9 September Kapitänleutnant Friedrich Guggenberger’s U-81 sank the 5,591-ton British Empire Springbuck straggling from the SC.42 convoy. During the afternoon U-85 intercepted the convoy close to Cape Farewell, failed in its first attempt to attack, but transmitted a sighting report that brought much of the 'Markgraf' wolfpack into range for attacks during the night of 9/10 September.

Oberleutnant Heinz-Otto Schultze’s U-432 sank the 5,229-ton British Muneric, U-81 failed to achieved any hit, Oberleutnant Georg-Werner Fraatz’s U-652 torpedoed two ships (the 6,508-ton British tanker Tahchee which was damaged and towed to port by the corvette Orillia and the 3,410-ton British Baron Pentland which was damaged and sunk later by Kapitänleutnant Heinz-Joachim Neumann’s U-372), Schultze’s U-432 sank the 3,205-ton Dutch Winterswijk and 1,113-ton Norwegian Stargard, Guggenberger’s U-81 sank the 3,252-ton British Sally Maersk, and Oberleutnant Siegfried Rollmann’s U-82 sank the 7,465-ton British CAM-ship Empire Hudson and fired a salvo that failed to hit Skeena). The fact that the corvettes of the escort remained behind to recover survivors facilitated the attacks of the U-boats. During the daylight hours of 10 September U-432 was the contact keeper.

Oberleutnant Eberhard Gregert’s U-85 made two attacks and sank the 4,748-ton British Thistleglen but was itself depth-charged and damaged by Skeena and Alberni. The arrival of the first air escort, a Consolidated Catalina flying boat of the RAF’s No. 209 Squadron from Iceland, forced U-501 to submerge. The Canadian corvettes Chambly and Moosejaw, despatched from St John’s, Newfoundland, to support the SC.42 convoy in its time of greatest danger, arrived from the west, and surprised and sank Förster’s U-501.

During the night of 10/11 September several U-boats again made attacks on the convoy. Rollmann’s U-82 sank the 7,519-ton British Bulysses and 3,915-ton British Gypsum Queen, Schultze’s U-432 sank the 1,231-ton Swedish Garm, Oberleutnant Hans Ey’s U-433 torpedoed and damaged the straggling 2,215-ton Norwegian Bestum, Meyer’s U-207 sank the 4,803-ton British Stonepool and 4,924-ton British Berury, and Rollmann’s U-82 torpedoed two ships, sinking 5,463-ton British Empire Crossbill and damaging the 1,999-ton Swedish Scania, which was sent to the bottom on the following day by Kapitänleutnant Hans-Heinz Linder’s U-202, which had made an earlier but unsuccessful attack.

During the morning of 11 September the corvettes Wetaskiwin, Mimose and Gladiolus and the trawler Buttermere, diverted from support of the HX.147 convoy, reached this convoy battle, and then Commander W. E. Banks’s British 2^nd Escort Group (destroyers Douglas, Veteran, Leamington, Skate and Saladin) arrived after refuelling at the Hvalfjörður in south-western Iceland once it had left the ON.13F convoy, rerouted to the north of SC.42 and now escorted only by the corvettes Anemone, Veronica and Abelia and the trawlers Vizalma and St Zeno. The US TU1.1.6 (destroyers Ellis, Cole, Broome and Simpson) was diverted from its task of escorting four ships from Reykjavik to Argentia and ordered to head to the south.

During daylight on 11 September aircraft of the RAF’s Nos 209 and 269 Squadrons, each based in Iceland, arrived over the convoy to provide much needed air cover. Veteran and Leamington depth-charged and sank Meyer’s U-207. U-432 continued with the convoy as the contact keeper. U-652 attacked without success and Kapitänleutnant Georg Schewe’s U-105 sank the 1,549-ton Panamanian Montana, an independent sailer.

During the night of 11/12 September the escort, now numbering 14 warships under the command of Banks and augmented by the trawler Windermere escorting a straggler, prevented the U-boats from delivering any successful attack, so while U-84 and U-43 launched torpedoes they both missed. By day on 12 September Skeena, Kenogami and Alberni had to detach to refuel at the Hvalfjörður, while the Canadian destroyers St Croix from the SC.41 convoy and Columbia from the HX.147 convoy joined the escort after refuelling. U-432, U-373 and U-433 maintained contact, but were held off by the escorts and aircraft. After a quiet night on 13 September the US destroyers Sims, Hughes and Russell reached the convoy, which made it possible for the 2^nd Escort Group’s five destroyers to refuel once more.

Fog now began to close, and in these conditions U-373, U-433, U-552, U-572 and U-575 could not locate the convoy. Skeena, together with five merchant vessels bound from Iceland to the UK, later rejoined the escort. On 14 September Chambly left for the Hvalfjörður and the three US destroyers were recalled, but only U-552 managed to re-establish contact before the Germans broke off the operation.