'Rossbach' was a U-boat wolfpack operation in the Atlantic against the ON.203, ONS.19, HX.258, ON.204, HX.259 and SC.143 convoys (24 September/9 October 1943).

The wolfpack comprised U-91, U-260, U-275, U-279, U-305, U-309, U-336, U-378, U-389, U-402, U-419, U-437, U-448, U-539, U-584, U-603, U-610, U-631, U-641, U-643, U-645, U-666, U-731, U-758, U-762 and U-952, and for the loss of Kapitänleutnant Otto Finke’s U-279, Kapitänleutnant Hans Hunger’s U-336, Kapitänleutnant Siegfried Heilmann’s U-389, Kapitänleutnant Dietrich Giersberg’s U-419, Kapitänleutnant Walter Freiherr von Freyberg-Eisenberg-Allmendingen’s U-610 and Kapitänleutnant Hans Harald Speidel’s U-643 sank only one 5,612-ton merchant vessel and the Free Polish destroyer Orkan.

The 'Rossbach' attack on the SC.143 convoy was the second battle in the German navy’s renewed offensive of the autumn of 1943 in the North Atlantic. Following the 'Leuthen' attack on the ONS.18 and ON.202, Grossadmiral Karl Dönitz, commander-in-chief of the German navy but still in day-to-day control of the U-boat arm via Konteradmiral Eberhard Godt, the service’s operations chief, was confident of success and therefore wished to press his boats' offensive. The U-boats already in the Atlantic were therefore reorganised into a new patrol line, the 12 remaining 'Leuthen' boats being joined by nine boats newly arrived from bases in France and Germany. These 21 boats were stationed at the western edge of the 'air gap' in the middle of the Atlantic, to the south of Greenland, with the task of intercepting eastbound convoys carrying war matériel for the invasion of Europe.

The Allies were also encouraged by the outcome of the battle for the ONS.18 and ON.202 convoys, and felt that they had the advantage over any new German attack. While forming, the 'Rossbach' force came under attack by air patrols, resulting in the loss of four boats and severe damage to another four, which had therefore to return to base. Three other boats were damaged to a lesser extent and were therefore able to continue operations, while a further two boats arrived as reinforcements.

The SC.143 convoy departed Halifax for Liverpool on 28 September, and comprised 39 merchant vessels and the warships of Lieutenant Commander R. Dyer’s Canadian Escort Group C2 (British destroyer Icarus, British frigate Duckworth, and Canadian corvettes Chambly, Drumheller, Kamloops, Morden, Sackville and Timmins [soon detached]). Also accompanying the convoy was the 8,017-ton merchant aircraft carrier Rapana, a tanker adapted with a deck able to accommodate four Fairey Swordfish anti-submarine aircraft.

By 6 October the wolfpack of 14 U-boats was deployed to intercept both the SC.143 convoy and the HX.259 expected westbound convoy. Admiral Sir Max Horton’s Western Approaches Command became aware of the wolfpack’s position via intelligence (principally 'Ultra' decrypts) but decided to engage the wolfpack and force a battle.

The HX.259 convoy was diverted to the south, and SC.143 was reinforced by Commander E. N. V. Currey’s 3^rd Support Group (destroyers (Musketeer, Oribi, Orwell and Free Polish Orkan) and allowed to continue toward the German submarines. Oberleutnant Werner Techand’s U-731 sighted SC.143 on 8 October as it was returning to base after sustaining damaged in an air attack but managed to send a sighting report, and throughout the day the 'Rossbach' boats converged on the reported position. Seven boats had gathered by evening, and at the fall of night mounted their initial attack.

During the night of 8/9 October Oberleutnant Otto Ferro’s U-645 torpedoed and sank the 5,612-ton US Yorkmar, and Kapitänleutnant Erich Mäder’s U-378 hit Orkan, which sank with the loss of 157 men: this was the worst naval loss suffered by the Free Polish navy during the war.

During the following day the convoy’s air cover was able to undertake several successful attacks. Three U-boats were attacked by aircraft during the day: Giersberg’s U-419 was attacked and sunk by a Consolidated Liberator of the RAF’s No. 86 Squadron; Speidel’s U-643 was damaged by another two Liberator patrol bombers of the RAF’s Nos 86 and 120 Squadrons, and later caught on the surface by another Liberator of No. 86 Squadron and sunk; and von Freyberg-Eisenberg-Allmendingen’s U-610 was attacked by a Short Sunderland flying boat of the RCAF’s No. 423 Squadron and sunk. Two other boats were damaged in air attacks and forced to return to base: these were Kapitänleutnant Hans-Jürgen Lauterbach-Emden’s U-539 attacked by a Liberator aeroplane of an unidentified squadron, and Kapitänleutnant Wolfgang Hille’s U-762 attacked by a Liberator of No. 120 Squadron.

Following this, Dönitz ordered the attack to be broken off, and the 'Rossbach' force, now reduced to just six boats, was disbanded.

The SC.143 convoy continued its voyage, and arrived without further loss at Liverpool on 12 October. Undeterred by the poor results of this attack, and its heavy losses, Dönitz nonetheless wished to press on with the U-boat offensive, so the remaining 'Rossbach' boats were reinforced as formed the basis of the new 'Schlieffen' wolfpack.