Escort Group B6: British destroyer HMS Viscount (D 92) (LtCdr J.V. Waterhouse, RN) until 27 August Norwegian corvettes HNoMS Acanthus (K 01), HNoMS Eglantine (K 197), HNoMS Montbretia (K 208) until 29 August and HNoMS Potentilla (K 214) until 26 August British rescue ship Stockport (Master Thomas Ernest Fea, OBE) fitted with HF/DF.

Joined on 26 August: Canadian destroyer HMCS St. Laurent (H 83) (LtCdr E.L. Armstrong, RCN) and American destroyer USS Bristol (DD 453) (LtCdr C.C. Wood, USN) until 29 August.

Joined on 27 August: Canadian corvettes HMCS Lunenburg (K 151) (T/Lt W.E. Harrison, RCNVR) until 28 August and HMCS Rosthern (K 169) (Cdr P.B. Cross, RCNVR) leaving the same day again.

Joined on 28 August: Canadian corvette HMCS Woodstock (K 238) (T/Lt L.P. Denny, RCNR).

Local escort relieved Escort Group B6 on 29 August: British destroyer HMS Georgetown (I 40) (LtCdr P.G. MacIver, DSO, RD, RNR), Canadian destroyer HMCS Niagara (I 57) (LtCdr R.F. Harris, RCNR) and Canadian corvettes HMCS Kenogami (K 125) (LtCdr R. Jackson, RCNVR) and HMCS Prescott (K 161) (T/Lt H.A. Russell, RCNR), the latter and HMCS Niagara leaving on 1 September.

Wolfpack Lohs: U-135 (Praetorius), U-174 (Thilo), U-176 * (Dierksen), U-256 (Loewe), U-373 (Loeser), U-438 * (Franzius), U-569 (Hinsch), U-596 (Jahn), U-604 * (Höltring), U-605 * (Schütze), U-660 (Baur), U-705 * (Horn) and U-755 (Göing), later joined by U-432 (Schultze)

* U-boats that fired torpedo or used the deck gun

The BdU had expected the sailing of convoy ONS-122 and positioned the 13 U-boats of wolfpack "Lohs" in a 300 mile long line in the naval grid AK. They were instructed to search to the north because the earlier ON convoys had all been rerouted closer and closer to Iceland and Greenland. CinCWA was aware of this by ULTRA and tried to evade the patrol line to the south, but due to a decryption error the southernmost boat, U-135, had not followed the other boats to the north and was outside of the line when they sighted the convoy on a southwesternly course in 52°25N/26°20W at 16.48 hours on 22 August. The U-boat was sighted by HNoMS Eglantine which chased her away on the surface for 3 hours. However she managed to regain contact with the convoy and shadow it until loosing the ships in mist and darkness during the night of 22/23 August even though her messages had been picked up by HF/DF and investigated by HNoMS Montbretia. Initially the BdU did not believe that the convoy was really ONS-122 until U-135 reported its change of course to the west and then he immediately ordered the whole group "Lohs" to attack regardless of the fuel situation, even with the northernmost boat U-660 over 300 miles away. U-660, covering the distance at full speed, made contact with the convoy after 33 hours.

On 23 August, U-432 coming from France joined the hunt but was distracted by a fast freighter sailing alone on a southerly course which she chased for several hours but then lost in fog and darkness. Due to this delay U-432 never made contact with the convoy. At 20.59 hours, U-705 reported the sighting of one of the convoy escorts and later the convoy itself. Her contact messages were picked up by HF/DF and HMS Viscount and HNoMS Potentilla went to investigate. Shortly after midnight they located this shadower, forced her to dive by gunfire and attacked with depth charges. During the attack both ships located the nearby U-135 by radar and also forced her to dive, then continued to attack both contacts for 4 hours before eventually rejoining the convoy. In these attacks HMS Viscount used her Hedgehogs, the first use of this newly developed weapon, but they were unsuccessful as all charges detonated prematurely after hitting the surface of the water. Observing a pattern of oil after the last attacks they claimed the destruction of one of the U-boats, in fact U-135 sustained minor damages and U-705 was more seriously hit with her stern tube out of action but both were able to continue the hunt. This night action was observed by U-256, U-373 and U-569.

At 09.25 hours on 24 August, U-660 located the convoy again and sent bearing signals for the other U-boats eventually leading U-605, U-438, U-373, U-569 and U-755 to the convoy in the afternoon before breaking off the chase because she was low on fuel. She continued the hunt shortly afterwards when the BdU radioed that all boats low on fuel would be refuelled from the tanker U-462 after the battle. At 14.52 hours, U-604 spotted a fast freighter sailing alone on a northerly zigzag course. This was the eastbound Abbekerk, which had been investigated only one hour earlier by HNoMS Eglantine southeast of the convoy ONS-122. The U-boat chased the ship for 13 hours and finally sank her, but was then ordered by the BdU not to participate in this convoy battle any more as she was too far east by then.

In the late afternoon five U-boats were in contact with the convoy and in the evening four more made contact, U-176, U-256, U-596 and U-705. At 17.55 hours, HNoMS Montbretia was sent to investigate a HF/DF bearing and sighted U-569 diving at some distance. Unable to obtain a contact the corvette kept her down until dusk and then returned to the convoy. At 19.22 hours, U-596 was sighted by HNoMS Potentilla on the starboard bow of the convoy. The corvette and HMS Viscount left the convoy to chase her, but the U-boat escaped by diving like U-569 which again had to dive when sighted by HMS Viscount at 21.04 hours. At 21.31 hours, the destroyer next picked up U-596 by ASDIC, made a Hedgehog attack which failed because it was fired five seconds too late and then dropped two depth charges before returning to the convoy. The U-boat was not damaged in the attack, but had a tense moment when she unintentionally plunged to a depth of 190 meters because the linkage to a flood valve jammed and a diving tank flooded uncontrollably. U-755 had evaded this hunt at high speed towards northeast and when she turned west again encountered HNoMS Potentilla which sighted her and U-174 at 21.54 hours. The latter boat had just made contact with the convoy and both U-boats were chased by the corvette to the north until U-174 turned east and U-755 west. HNoMS Potentilla stayed with the westbound one and fired its 4in gun, but the shots fell short and U-755 escaped at high speed to the northwest in the darkness.

At midnight HMS Viscount rejoined the convoy ONS-122 and the SoE realized that the situation looked grim, knowing from HF/DF bearings that the four escorts currently with the convoy were outnumbered by at least seven U-boats with another two held off by HNoMS Potentilla. The SoE correctly assumed that the U-boats would attack during the night from the darker starboard side so he positioned HNoMS Montbretia on the starboard bow and HNoMS Eglantine on the starboard beam, with HMS Viscount zigzagging astern of the convoy and HNoMS Acanthus alone on the moonlit port side of the convoy. At 01.00 hours on 25 August, the convoy changed its course from southwest to west. After this move U-373 found herself on the port bow of the convoy, U-176 directly ahead and U-438 and U-605 on the starboard bow in favorable attack positions.

About 01.30 hours on 25 August, the moon disappeared behind clouds and all three U-boats on the starboard side began their attack runs. The first was U-605 firing all five torpedo tubes in single shots at overlapping ships in the starboard columns from the rather long distance of about 4000 meters between 01.38 and 01.41 hours. They observed three hits and heard a further detonation, claiming two ships sunk and another damaged. Originally the convoy had 10 columns but was reformed later into 9 and it was the outermost starboard column which was hit in this attack. The first torpedo hit Katvaldis in station #92. She had originally been in station #91 but was ordered the evening before the attack to exchange her station with Ingerfire in #92 because the latter vessel had constantly lagged behind. The next ship hit was Sheaf Mount in station #94, which broke in two and sank in flames within a minute after being struck by one or two torpedoes. The SoE ordered HNoMS Montbretia and HNoMS Eglantine to carry out a “Raspberry” operation to starboard and the convoy to make an emergency turn of 45° to port. Stockport left her station to begin her rescue work. At 01.57 hours, U-176 and U-438 had both reached their attack positions and simultaneously fired torpedoes. U-176 fired a spread of two torpedoes from ahead of the convoy and both hit Empire Breeze in station #41. U-438 fired one torpedo from between the starboard columns and observed a ship sinking by the stern 3 minutes after being hit, apparently mistaking the success of U-176 for her own because this torpedo was seen to miss astern of Athelprince in station #51. The U-boat then turned around and fired its stern torpedo, sinking the Trolla in station #71 and fired the last ready bow torpedo after another turn which missed but was thought to have hit a ship beyond. The Empire Breeze was abandoned by the crew but remained afloat and was reboarded the next morning.

HMS Viscount first examined the wreckage of Sheaf Mount and then went ahead of the convoy to help HNoMS Acanthus which reported a RDF contact ahead. This was U-373 which tried to get from the moonlit port side to the darker starboard side for an attack, but was forced to dive by the corvette with two rounds from her 4in gun and unsuccessfully attacked with five depth charges at 02.20 hours. HNoMS Acanthus lost contact after the attack and went back to her station. At 02.12 hours, U-176 fired one stern torpedo at HMS Viscount after being located by radar and missed astern because it became a surface runner. The destroyer engaged the crash-diving enemy by dropping five depth charges without damaging her. Turning for another attack HMS Viscount spotted U-605 which also dived after a short hunt and she attacked with five depth charges, but then lost contact and returned to the convoy. U-438 had observed this attack while reloading her torpedo tubes on the surface and had to evade the destroyer at full speed on the surface. HNoMS Montbretia returned to her station on the starboard bow of the convoy after carrying out “Raspberry” without sighting a U-boat, but obtained an ASDIC contact and attacked with five depth charges at 02.35 hours. The target of this attack was U-605 which only received minor damage.

When HNoMS Eglantine returned to the convoy after “Raspberry”, also carried out without sighting a U-boat, she obtained a radar contact which proved to be the still floating bow of Trolla with survivors in a lifeboat and on a raft nearby. The corvette slowed down to pick them up, but got another radar contact astern of the wreck and went off to investigate this first. It proved to be a U-boat, which was forced to dive by gunfire and attacked with only a single depth charge at 02.47 hours because the throwers misfired and the trap jammed. The corvette made two more attacks dropping eight and ten depth charges, then lost contact and returned to the convoy. The U-boat attacked was probably U-256 which plummeted to a depth of 200 meters when 17 tons of water entered the stern through a damaged exhaust pipe. The U-boat managed to surface after 30 minutes and escaped on the surface, but had to abort the patrol because one battery and the compressors were out of action.

Around this time thick fog set in, reducing the visibility to 600 meters and later to less than 300 meters. HNoMS Potentilla was still returning to ONS-122 when it was attacked and was ordered to screen Stockport rescuing survivors astern of the convoy. Soon they located the wreck of Empire Breeze by radar but did not see her survivors when circling the ship. Not far away the rescue ship was located, which just had picked up all survivors from Katvaldis and Sheaf Mount and was now looking for the survivors of the other torpedoed ships. The corvette went alongside of Stockport but few minutes later obtained another radar contact and sighted a U-boat closing the rescue ship at slow speed. This was U-605 which had loaded her last torpedo and was now looking astern of the convoy for damaged ships. At 04.25 hours, the U-boat was surprised by HNoMS Potentilla approaching at full speed out of the thick fog and taken under heavy fire from all available weapons. HNoMS Potentilla observed one hit from her 4in and many hits from her AA guns. The corvette had intended to ram but missed by a narrow margin because the gun flash had blinded the men on the bridge. They were so close that the Germans could be seen and their cries heard. U-605 immediately crash-dived at a steep angle and fell to a depth of 170 meters, out of reach of the three depth charges dropped just astern and the six that followed in a second attack. They had to isolate the conning tower because it slowly flooded until eight tons of water had entered the boat. When they surfaced four hours later an examination showed 30 hits from gunfire. With U-boats in close proximity and the thick fog persisting, Stockport gave up her search for survivors and returned to the convoy alone.

Her own depth charge explosions had disabled the ASDIC of HNoMS Potentilla and she circled the area while making repairs. While doing so her lookouts spotted the survivors in the lifeboat and the raft from Trolla, which had earlier been left behind by HNoMS Eglantine and she stopped to pick them up. In this vulnerable situation another radar contact of a vessel at a distance of 2 miles and approaching fast was reported. The commander urged his men to hurry up and they finished the rescue work when the contact was only a half mile away, then turned the corvette at full speed towards it and soon sighted U-174 at 05.21 hours. They completely surprised the U-boat and opened fire with all weapons, observing one of five 4in rounds hit the base of the conning tower and several hits from the AA guns, but HNoMS Potentilla again missed ramming the U-boat by a few meters. Turning astern of U-174 and coming up along her port side, she dropped five depth charges so close that the charge from the starboard thrower was fired over the crash-diving U-boat and detonated on her starboard side while the others detonated on her port side. Shortly afterwards the corvette dropped four depth charges ahead of the swirl and then circled the area for one hour without obtaining an ASDIC contact. Because the area was littered with wreckage and oil from ships sunk from the convoy no traces could be attributed to the U-boat. U-174 surfaced more than 5 hours later and examined the damage. Several hits were found in the upper deck and the conning tower as well as a leak in the galley and some untraceable damage that left a trail of oil behind the boat forcing the commander to abort the patrol.

Around the same time HMS Viscount encountered a surfaced U-boat in the fog while returning to the convoy and attacked it twice with depth charges until loosing contact. The destroyer carried out a box search and obtained a radar contact, assuming that it was the same U-boat that tried to escape on the surface and forced it to dive by gunfire and attacked once with depth charges at 06.13 hours. In fact, the first attack was probably carried out on U-705 and the second was on U-176, both escaping damage. At 07.10 hours, HNoMS Eglantine surprised U-438 in thick fog on the starboard quarter of convoy ONS-122 and carried out three attacks which were hampered by traps that jammed and throwers that misfired, only dropping eight depth charges instead the intended 25. Still the U-boat was forced to surface due to flooding of the bow compartment but this was not noticed by the escorts and U-438 managed to escape in the fog. The fog also helped one of the stragglers, the British steam tanker Gloxinia (Master S.N. Fletcher), to escape after being missed by a spread of two torpedoes from U-705 at 08.50 hours.

While returning to the convoy, HNoMS Potentilla picked up another radar contact at 11.10 hours and tried to surprise U-569 coming out of the fog at full speed, but her gunners opened fire without orders and the U-boat escaped by crash-diving before the corvette was close enough and was not damaged by the three depth charges subsequently dropped. It was the fifth U-boat engaged by the corvette which was now almost out of depth charges and she left to return to the convoy but only found HMS Viscount which was also searching for the convoy. At 14.31 hours, HNoMS Potentilla obtained yet another radar contact and the faster destroyer went off to investigate, sighting U-660 on the surface. To avoid ramming damage, HMS Viscount gave away the element of surprise and opened fire but then spoiled the first approach for a depth charge attack and only dropped five depth charges after the U-boat had dived. Both escorts were unable to regain contact, so the destroyer had to give up a planned Hedgehog attack. They continued their search for the convoy and rejoined at 20.00 hours. The last attack by the escorts was carried out by HNoMS Montbretia on the port side of the convoy. After obtaining an ASDIC contact at 17.29 hours, she carried out two attacks with 15 depth charges and then lost contact in the wake of the convoy – this was probably on a non-sub target as no U-boats were in contact with the convoy at that time.

By the evening of 25 August, all escorts and the rescue ship had returned to the convoy which now consisted of 25 ships – four had been sunk and the rest had lost contact during the emergency turn in thick fog and became stragglers. The next night passed without incident and in the morning a Surgeon Lieutenant, who was a passenger, was transferred from HNoMS Acanthus to HNoMS Potentilla to take care of the badly injured survivors from Trolla. HNoMS Potentilla had to remain with the convoy until reinforcements arrived in the form of HMCS St. Laurent and USS Bristol at 19.30 hours and then immediately left to bring the survivors to a hospital at St. Johns, arriving on 27 August. Unfortunately this was too late for one of the men who died on 28 August. HMS Viscount transferred command to HMCS St. Laurent and stayed with the convoy for the night, leaving the next morning for St. Johns and arriving with only 10 tons of fuel remaining. On 27 August, HMCS Lunenburg and HMCS Rosthern arrived and the latter was sent to search for the Empire Breeze and to screen the tug HMS Frisky (W 11) which was sent from St. Johns to salvage the still floating ship on 26 August. The search by both ships proved to be fruitless and they returned to port on 30 August, not knowing that the Empire Breeze had probably foundered a few hours after the Irish steam merchant Irish Willow had picked up her survivors on 27 August.

At 12.00 hours on 26 August, the BdU ordered all U-boats to break off the operation against convoy ONS-122 because the contact had been lost in the fog that persisted throughout the day. The thick fog had certainly saved the convoy from greater losses as only three U-boats were able to attack before the visibility was reduced to less than 300 meters, claiming five ships sunk totalling about 26,000 GRT and hits on three more ships – in fact, four ships totalling 17,235 GRT were sunk. Escort Group B6, although under strength because HMS Ramsey (G 60) (LtCdr R.B. Stannard, VC, RNR) had to return to port with defects, fought well and made good use of HF/DF to keep several U-boats away from the convoy, even when the corvettes actually proved to be too slow to catch them on the surface. The biggest advantage proved to be the new Type 271 centimetric radar fitted to all escorts, which made it possible to carry out surprise attacks on the U-boats in thick fog. The Hedgehog was another new weapon used by HMS Viscount in this battle, but due to the lack of experience no successful attack was carried out with it. The escorts claimed four U-boats badly damaged or probably sunk. In fact, none of the 14 participating U-boats (10 on their first war patrol) were lost but eight were damaged of which two had to abort their patrols (U-174 and U-256) and two more were ordered to return to base because they were low on fuel and no longer fully operational (U-438 and U-605).