'Leuthen' (i) was a U-boat wolfpack operation in the Atlantic against the ON.202 and ONS.18 convoys (15/24 September 1943).

This wolfpack was formed, probably on 23 August, with 21 U-boats, and was involved mostly in a convoy action around the ON.202 convoy late in September 1943. Oberleutnant Dietrich Epp’s U-341 was sunk on its way to join the group, U-274 and U-963 suffered ice damage and had to turn back, and finally U-413 suffered mechanical problems and had also to abort. The wolfpack thus comprised U-229, U-238, U-260, U-270, U-274, U-305, U-338, U-341, U-377, U-378, U-386, U-402, U-413, U-422, U-584, U-641, U-645, U-666, U-731, U-758, U-952 and U-963, and for the loss of Oberleutnant Robert Schetelig’s U-229, Kapitänleutnant Manfred Kinzel’s U-338 and Epp’s U-341 sank 10 ships (41,227 tons including the Canadian destroyer St Croix, British frigate Itchen and British corvette Polyanthus) and damaged three other ships (including the British frigate Lagan which was declared a total loss) in attacks on the ON.202 convoy.

This was the first occasion on which U-boats fired the G7es/T5 Zaunkönig acoustic-homing torpedo.

The ONS.18 and ON.202 Allied convoys became embroiled in a major battle with a U-boat wolfpack between 19 and 23 September. The battle was the first after 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, had ordered an autumn offensive against the Allies' transatlantic convoy operations after the service had regrouped in the aftermath of its defeat in the 'Black May' of 1943. Following the defeats of May 1943, and the devastating losses incurred by the U-boat arm, Dönitz had withdrawn his U-boats from attacks on the North Atlantic route while awaiting tactical and technical improvements. By September 1943 these were ready, and Dönitz despatched the 'Leuthen' (i) wolfpack of 21 boats to renew the attack on the North Atlantic route.

The new pack established a patrol line of 21 U-boats in the area to the south of Greenland in the location at which it could intercept and destroy westbound convoys as they were about to enter the Greenland 'air gap', in which Allied aircraft were reckoned unable to operate for lack of the required range. The 'Leuthen' (i) wolfpack was to harry any westbound convoy it encountered while crossing the gap, before breaking off to repeat the onslaught against an eastbound convoy.

On 12 September the ONS.18 convoy departed Liverpool bound for Halifax, Nova Scotia. The convoy comprised 27 merchant ships, and was protected by Commander M. J. Evans’s British Escort Group B3 (destroyers Keppel and Escapade, frigate Towey, and corvettes Narcissus, Orchis, and Free French Roselys, Lobélia and Renoncule). The convoy was also accompanied by the first merchant aircraft carrier, Empire MacAlpine, a 7,940-ton grain ship adapted with a small flight deck and limited facilities for the operation of four fighters.

When Admiral Sir Max Horton’s Western Approaches Command became aware of the presence of the 'Leuthen' (i) wolfpack, it decided to reinforce the ONS.18 convoy: the following ON.202 convoy was therefore instructed to close up, and Commander C. E. Bridgman’s Canadian 9^th Support Group (destroyer St Croix, British frigate Itchen, and corvettes Chambly, Morden and Sackville) was despatched to supplement the defence. ON.202 had left Liverpool on 15 September with 38 merchant ships and escort provided by Lieutenant Commander P. W. Burnett’s Canadian Escort Group C2 (destroyers Gatineau and British Icarus, British frigate Lagan, and corvettes Drumheller, Kamloops and British Polyanthus).

In total, therefore, the two convoys comprised 65 merchant ships escorted by 19 warships, and faced an attack by 21 U-boats.

On 19 September the ONS.18 convoy was sighted by Kapitänleutnant Paul-Friedrich Otto’s U-270, which sent a sighting report and received permission to attack. U-270 fired an acoustic-homing torpedo, which was a new weapon just entering operational service, at Lagan, and this damaged the warship’s stern. The escorts counterattacked but U-270 escaped, though Escapade was damaged by a misfire from her 'Hedgehog' anti-submarine spigot mortar launcher. Both Lagan and Escapade were forced to detach, returning to base under escort.

The U-boats of the 'Leuthen' (i) packed concentrated during 19 September, but two of the boats were attacked by air patrols which, following the introduction of a number of very-long-range Consolidated Liberator patrol bombers during the summer, had been extended into the mid-Atlanic 'air gap'. Epp’s U-341 was attacked and sunk by a Consolidated Liberator long-range patrol bomber of the Royal Canadian Air Force’s No. 10 Squadron. Kinzel’s U-338 was attacked by a Liberator of the RAF’s No. 120 Squadron, which was credited with the kill. Post-war analysis showed that U-338 had been only damaged in this attack, however, and was later engaged and sunk by the corvette Drumheller of the Escort Group C2.

On the night of 19/20 September several boats of the 'Leuthen' (i) wolfpack made contact. Kapitänleutnant Hubertus Purkhold’s U-260 attacked but gained no hits. Kapitänleutnant Horst Hepp’s U-238 fired on two ships, sinking the 7,176-ton US Theodore Dwight Weld and damaging the 7,176-ton US Frederick Douglass, which fell out of the convoy and was sunk later in the day by Oberleutnant Otto Ferro’s U-645.

On 20/21 September a dozen boats were in contact, and eight were able to attack. Kapitänleutnant Rudolf Bahr’s U-305 hit St Croix, which sank with the loss of 66 of her crew. Kapitänleutnant Oskar Curio’s U-952 torpedoed Polyanthus, which exploded and sank, leaving only one survivor who, with 81 men from St Croix, was rescued by Itchen. Oberleutnant Fritz Albrecht’s U-386 was depth-charged and damaged, and forced to retire. Oberleutnant Rudolf Batz’s U-603 was ordered to rendezvous but was prevented by air attacks from complying.

The U-boats of the 'Leuthen' (i) pack remained in contact, and on the night of 21/22 September renewed their attack. Oberleutnant Ernst-August Gerke’s U-377 attacked, claiming hits, but these were not confirmed and, after being damaged by air attack, retired. Kapitänleutnant Paul Siegmann’s U-230 attacked, but again no hits were confirmed, and This boat too came under attack, in this instance by an unidentified escort, and forced to retire. Schetelig’s U-229 was attacked and destroyed, this being credited to Keppel. Oberleutnant Wolfgang Poeschel’s U-422 was damaged by air attack, but was able to continue.

On 23 September the combined convoys reached the area of the Grand Banks, where fog hindered visibility for both the air patrols and the U-boats of the 'Leuthen' (i) wolfpack. U-238 was able to penetrate the escort screen and sank the 5,096-ton Norwegian Skjelbred, 3,642-ton Norwegian Oregon Express and 7,134-ton British Fort Jemseg. Kapitänleutnant Herbert Engel’s U-666 torpedoed Itchen, which sank, leaving just three survivors from her own crew and those of Polyanthus and St Croix she had earlier rescued. U-952 sank the 6,198-ton US Steel Voyager and damaged the 7,176-ton US James Gordon Bennett. Kapitänleutnant Helmut Manseck’s U-758 attacked, but had no confirmed hits and was itself depth-charged and damaged.

Poor visibility, fuel shortages and fatigue now beset both the U-boats and the escorts, and the U-boat command, believing the attack to have been a great success, ordered the U-boats of the 'Leuthen' (i) wolfpack to break off their attack. Claims by the various U-boats amounted to 12 escorts and nine merchant ships sunk, as well as another two ships damaged, but the actual losses were three escorts and six merchant ships sunk as well as one escort and one merchant ship damaged, while three U-boats had been sunk and another three damaged and forced to return to base.

Both convoys continued to their destinations, the ONS.18 convoy reaching Halifax on 29 September, and the ON.202 convoy reaching New York on 1 October.

Believing the new tactics and weapons successful, the U-boat command continued the offensive. The 'Leuthen' (i) wolfpack was disbanded, with 12 boats forming the new 'Rossbach' wolfpack which was joined by nine fresh U-boats to attack the next set of eastbound convoys.

In the UK, the Admiralty was also encouraged by the result of this convoy battle. Despite the losses, the great majority of the merchant ships had arrived safely. While in themselves serious, the losses were no more grievous than during the battles late in 1942 and early in 1943. Thus the Admiralty was confident the escorts would be able to meet the challenge of the U-boat arm’s new weapons and tactics.