'ON' (ii) was the designation of Allied convoys (together with a numerical suffix) plying the route from Liverpool in the UK to Halifax, Nova Scotia, and as such successors to the 'OB' series and as such reciprocals of the 'HX' and 'SC' series (July 1941/June 1945).

There were 307 such 'Outbound to North America' convoys, which alternated fast and slow convoys until the inauguration of the ONS convoys for slower ships.

From 7 September 1939 the 'OB' convoys departed Liverpool to the south through St George’s Channel to the open Atlantic. Off Land’s End the convoys were joined by 'OA' convoys from London on the estuary of the Thames river via the English Channel. The combined 'OA' and 'OB' convoys were escorted for about four days to get beyond the range of U-boat patrols before the ships dispersed, 865 miles (1390 km) to the west of Land’s End, to make passage to their individual destinations. After the fall of France in June 1940, 'OA' and 'OB' convoys sailed to the north to join in the Western Approaches. As German aircraft, surface warships and U-boats were able to extend their reach farther into the Atlantic from bases in occupied France, ships formerly assigned to the 'OA' and 'OB' convoys were then formed into 'ON' convoys departing Liverpool via the North Channel and escorted all the way to Halifax, Nova Scotia.

These convoys were numbered from ON.1, which departed on 26 July 1941 with 55 merchant vessels and an eventual total of 15 escorts to disperse on 9 August, to ON.305, which sailed on 27 May 1945 with 76 merchant vessels and an eventual total of 16 escorts to arrive on 10 June.

From August 1942 the Mid-Ocean Escort Force of British and Canadian warships, together with a few US Coast Guard cutters, escorted ON convoys to meet the Royal Canadian Navy’s Western Local Escort Force off Halifax, and the WLEF escorted most convoys from ON.125 to ON.301 forward to New York City. Most of the ships in the ON convoys were in ballast, although some carried coal or other export goods, and a total of 14,864 ships sailed in 307 ON convoys. One ON convoy sailed in fast and slow sections, and two others were cancelled. U-boats sank 81 of these ships, and another 23 were lost as a result of accidents at sea. (These figures do not include stragglers, although the majority of casualties to U-boats were ships that had fallen out of convoys or were sailing independently). Some 10 warships were also lost while escorting ON convoys.

The ON.67 convoy of 40 ships departed Liverpool on 14 February 1942 with the convoy rescue ship Toward, and was escorted to the Mid-Ocean Meeting Point by the British Escort Group B4. On 19 February Commander Albert C. Murdaugh’s US Task Unit 4.1.5, whose ships had no previous experience of working together, assumed responsibility with the destroyers Bernadou, Edison, Lea and Nicholson, and the Canadian corvette Algoma. U-155 spotted and reported the convoy on 21 February. Toward obtained a bearing on the contact report, and Lea made an unsuccessful search at dusk. The U-boat approached the port quarter of the convoy before dawn on 22 February and sank the 7,984-ton British tanker Adellen and 1,799-ton Norwegian freighter Sama: Algoma rescued 11 of the Adellen's 31-man crew, and Nicholson and Toward found 20 of the Sama's 40-man crew. The U-boat crash-dived to avoid Bernadou, which had in fact not spotted the boat, and made another crash-dive while shadowing the convoy at 10.42, when Edison also failed to detect it.

U-69, U-558 and U-587 found the convoy on 23 February. Kapitänleutnant Günther Krech’s U-558 approached the convoy at 21.20, but repeatedly turned away to avoid Bernadou's patrols until a squall provided cover at midnight, and then torpedoed the 5,578-ton Norwegian tanker Inverarder at 00.45 on 24 February, the tanker sinking slowly, and Toward rescued all 42 of her crew. U-558 made another approach at 02.30 and fired a single torpedo at Edison: the torpedo missed, and the ship’s crew was unaware it had been targeted. U-558 torpedoed and sank the 9,432-ton Norwegian tanker Eidanger at 02.55. U-558 reloaded and at 05.50 torpedoed the 8,009-ton British tanker Anadara, 9,551-ton Norwegian tanker Finnanger, and 4,365-ton British freighter White Crest: all three ships were damaged, straggled and were sunk.

Kapitänleutnant Erwin Rostin’s U-158 located the convoy at 04.25 on 24 February and torpedoed the 8,032-ton British tanker Empire Celt, which was testing a new Admiralty defence system by streaming a strong steel net from 50-ft (15-m) poles along each side of the ship. One torpedo broke through the net and hit amidships. Empire Celt later broke in half, but a tug from Newfoundland rescued 31 of the 37-man crew. As U-558 was torpedoing ships on the starboard side of the convoy, U-158 approached the port side and torpedoed the 8,146-ton British tanker Diloma at 06.35. The tanker was the only torpedoed ship to reach Halifax. Both U-158 and U-558 then submerged to avoid being seen in the early daylight.

U-558 found and sank the drifting and abandoned Eidanger astern of the convoy with gunfire and a torpedo. Lea investigated a direction-finder bearing from Toward at 15.15 and spotted U-558 some 20 miles (32 km) astern of the convoy at 17.07. Lea dropped eight depth charges at 17.46, and then surprised the U-boat on the surface at 18.13 and dropped 14 depth charges at 18.47. U-558 was undamaged. Nicholson investigated a direction-finder bearing from Toward and sighted U-158 at 13.23. The boat dived and evaded Nicholson, which slowed to listen. U-158 surfaced at 15.50 and was surprised to find Nicholson waiting only 1,650 yards (1500 m) distant and then crashed-dived before Nicholson saw it. U-158 surfaced again at 18.17 and was surprised to find Edison 2,000 yards (1830 m) away, and again avoided detection by crash-diving. Edison finally spotted U-158 making another approach to the convoy at 20.08 and dropped 25 depth charges over the following six hours. U-158 was undamaged, but had been prevented from making further attacks on the convoy.

Vizeadmiral Karl Dönitz ordered his U-boats to discontinue the attack on 25 February, and on the following day the escort was reinforced by the arrival of the US Coast Guard cutter Spencer. The convoy’s surviving ships reached Halifax on 1 March.

The 35 ships of the ON.127 convoy departed Liverpool on 4 September 1942 and were met at about 12.00 on the next day by Lieutenant Commander A. H. Dobson’s Canadian Escort Group C4 (destroyers Ottawa and St Croix, and corvettes Amherst, Arvida, Celandine and Sherbrooke). Even as the convoy departed Liverpool, the 'Vorwärts' wolfpack was forming some 500 miles (805 km) to the west of Ireland with U-91, U-92, U-96, U-211, U-218, U-380, U-404, U-407, U-411, U-584, U-594, U-608 and U-659, which established a search line across the convoy’s path just beyond the range of Allied land-based aircraft. U-584 spotted and reported the convoy on 9 September, but lost contact that evening. Oberleutnant Hans-Jürgen Hellriegel’s U-96 regained contact on 10 September and torpedoed the 6,313-ton Norwegian tanker Sveve, 12,190-ton US tanker F. J. Wolfe, and 4,241-ton Belgian freighter Elisabeth van Belgie in a single submerged daylight attack.

Sherbrooke fell back to aid the torpedoed ships while St Croix, Ottawa and Celandine searched unsuccessfully for U-96. F. J. Wolfe was able to regain her station, and Ottawa continued to patrol astern of the convoy after St Croix and Celandine had resumed their normal patrol stations. A co-ordinated night attack began as Oberleutnant Hans Stock’s U-659 torpedoed the 8,029-ton British tanker Empire Oil on the evening of 10 September. St Croix made sonar contact immediately before the attack and Celandine, Ottawa and St Croix searched for U-659 after the attack. St Croix and Ottawa fell back to rescue 23 of the stricken tanker’s 41-man crew.

Kapitänleutnant Otto von Bülow’s U-404 torpedoed the 7,417-ton Norwegian tanker Marit II, U-608 fired but missed, Kapitänleutnant Richard Becker’s U-218 torpedoed the 7,361-ton Norwegian tanker Fjordaas, and U-92 and U-594 both fired and missed before Ottawa, St Croix and Celandine rejoined the convoy. Sherbrooke remained astern of the convoy aiding the ships torpedoed by U-96, and rescued all but one of the crew of the sinking Sveve and Elisabeth van Belgie. The remaining escorts counterattacked, and depth-charge damage forced U-218 and U-659 to return to port. Both Marit II and Fjordaas were able to regain their stations, but Empire Oil fell back and was sunk by Kapitänleutnant Joachim Deecke’s U-584. None of the escort vessels' radar equipments was functional on 11 September. U-584 torpedoed the 4,884-ton Norwegian Hindanger in a submerged daylight attack as St Croix investigated a visual sighting 6 miles (10 km) away. Amherst fell back and rescued all but one of Hindanger's crew. The arrival of a Consolidated Liberator long-range patrol bomber of the RAF’s No. 120 Squadron prevented further daylight attacks on 11 September, but Hellriegel’s U-96 sank a 415-ton Portuguese sailing trawler by gunfire in the vicinity of the convoy. Then, in co-ordinated night attacks, U-380 missed with a salvo of four torpedoes, Kapitänleutnant Karl Hause’s U-211 torpedoed the 13,797-ton British whale factory ship Hektoria and 6,849-ton British freighter Empire Moonbeam, U-92 missed Ottawa with four torpedoes, and von Bülow’s U-404 torpedoed the 9,272-ton Norwegian tanker Daghild before Amherst and Sherbrooke rejoined the convoy. Daghild maintained station in the convoy, and Arvida rescued all but four of the 140 crewmen from Hektoria and Empire Moonbeam before those ships were sunk astern of the convoy by Kapitänleutnant Rolf Struckmeier’s U-608.

Excellent visibility on 12 September allowed a close forward screen of four escorts to discourage U-boats sighted up to 7 miles (11.25 km) away. U-407 and Kapitänleutnant Friedrich Mumm’s U-594 launched torpedoes unsuccessfully during the night, but later sank the straggling 6,131-ton Panamanian freighter Stone Street as the convoy came within range of Canso patrol bomber flying boats of the RCAF from Botland, Newfoundland, on 13 September when, at dusk, the escort was reinforced by the destroyers Annapolis and British Witch of the Newfoundland-based Western Local Escort Force. Both Kapitänleutnant Heinz Hungershausen’s U-91 and U-411 launched torpedoes unsuccessfully, and U-91 torpedoed Ottawa in the pre-dawn hours of 14 September, the destroyer sinking with 114 of her crew.

The rest of the convoy reached New York City on 20 September.

The ON.154 convoy of 47 ships departed Liverpool on 18 December 1942, and were met by the Canadian Escort Group C1 (destroyer St Laurent and corvettes Battleford, Chilliwack, Kenogami, Napanee and Shediac). The convoy also included the convoy rescue ship Toward, the 7,087-ton British replenishment oiler Scottish Heather and the 2,456-ton French-crewed special service vessel Fidelity. This last was a Q-ship armed with four 4-in (102-mm) guns, four torpedo tubes and a defensive torpedo net, and also carried two landing craft (LCV-752 and LCV-754), two Vought OS2U Kingfisher floatplanes and MTB-105.

The convoy, which steamed in a formation 5 miles (8 km) wide and 1.5 miles (2.4 km) long, had 12 columns each of three or four ships. Routed to the south in order to avoid storms, the convoy was more distant from other escort support groups and out of range of Allied patrol bombers for longer than was typical of most convoys. U-662 sighted and reported the convoy on 26 December, and during that night Oberleutnant Günther Ruppelt’s U-356 torpedoed the leading ships from two of the starboard columns: the 5,952-ton British Empire Union was hit at 01.40 and the 2,473-ton British Melrose Abbey II 10 minutes later, both ships sinking at about 02.30. Toward rescued 63 survivors from the first ship and 47 from the second. In a second attack, U-356 torpedoed the 7,051-ton Dutch freighter Soekaboemi at 04.10 and the 5,224-ton British freighter King Edward at 04.15. The latter sank within three minutes.

U-356 was thnen detected by the escorts and sunk with no survivors following depth-charge attacks by St Laurent, Chilliwack, Battleford and Napanee.

At dawn Toward rescued 25 men from King Edward and assisted Napanee in recovering all but one of the crew of Soekaboemi, which remained afloat when abandoned at 07.30. Oberleutnant Wolfgang Leimkühler’s U-225 began stalking Scottish Heather as she refuelled escorts 15 miles (24 km) astern of the convoy on the afternoon of 27 December, and was twice driven off by Chilliwack before hitting the oiler with a single torpedo in the boat’s third approach at 20.40. The ship was temporarily abandoned, but the second mate re-boarded her with 10 men and sailed the ship out of the danger zone. At dawn he returned and made a search for lifeboats before returning to the UK independently after recovering all of her crew.

U-260 started to shadow the convoy during the morning of 28 December and directed 18 U-boats to the convoy. Fidelity attempted to launch a Kingfisher floatplane, but this capsized and sank at 19.15. While St Laurent rescued the floatplane’s crew, a co-ordinated night attack began with U-boats entering the starboard side of the convoy at 19.58. Kapitänleutnant Hans-Jürgen Zetzsche’s U-591 torpedoed the 5,701-ton Norwegian freighter Norse King at 20.00. Leimkühler’s U-225 torpedoed two British freighters, the 5,273-ton Melmore at 20.03 and 5,083-ton Ville de Rouen at 20.05. Kapitänleutnant Hubertus Purkhold’s U-260 torpedoed the 4,893-ton British freighter Empire Wagtail at 20,45. As Empire Wagtail blew up in a single explosion with all of her crew, Fidelity reported a main engine failure, and Shediac was sent to assist her 2 miles (3.2 km) astern of the convoy.

U-boats then entered the port side of the convoy’s formation. Kapitänleutnant Horst Dieterichs’s U-406 torpedoed two British freighters, the 5,029-ton Lynton Grange at 21.20 and 4,871-ton Zarian at 21.23, and then moved to torpedo the 3,385-ton British freighter Baron Cochrane at 21.24. Korvettenkapitän Wolfgang Hermann’s U-662 torpedoed the damaged Ville de Rouen again at 22.10 and Leimkühler’s U-225 torpedoed the convoy commodore’s ship, the 7,068-ton British freighter Empire Shackleton, at 22.15 and the 4,919-ton Belgian freighter President Francoui at 22.30. Disabled ships were also being attacked astern of the convoy. Baron Cochrane was sunk at 21.50 by Oberleutnant Horst von Schroeter’s U-123 and Oberleutnant Heinrich Hasenschar’s U-628 sank Lynton Grange a few minutes later, both ships having been abandoned by their crews when they were hit earlier. U-123 and Kapitänleutnant Siegfried Strewlow’s U-435 sank Empire Shackleton at 22.55. Zetsche’s U-591 sank the abandoned Zarian just before 24.00. Shediac was ordered to leave Fidelity 30 miles (48 km) astern and rejoin the convoy while searching for survivors: she rescued 35 survivors from Melmore Head and 71 from Ville de Rouen between 03.10 and 03.30 and 24 from Empire Shackleton at 05.30 before rejoining the convoy at 13.00 short of fuel and with inadequate provisions for the number of survivors aboard. Two lifeboats abandoned the damaged President Francoui, but the remainder of the crew attempted to sail independently to the Azores. U-225 torpedoed the ship again at 06.30, and she was sunk at 09.30 by Kapitänleutnant Hans Hunger’s U-336. The damaged Norse King was similarly attempting to reach the Azores when she was sunk by U-435 at 15.07. There were no survivors.

The convoy escort was reinforced by the British destroyers Meteor and Milne at 14.00 on 29 December after they had rescued 42 survivors from Baron Cochrane at 07.00, 52 survivors from Lynton Grange at 07.20 and 49 survivors from Zarian at 08.15. Fidelity managed to get under way once more at 05.00 and declined the offer of a tug despatched from Gibraltar, but her speed was limited to 2 kt while streaming anti-torpedo nets at the time she was seen by Meteor and Milne at 05.30. Kapitänleutnant Ralph Kapitzky’s U-615 found the Q-ship while her main engines were again stopped for repairs between 10.15 and 11.00, but identified her as a Q-ship and therefore shadowed her with caution. A reconnaissance flight by Fidelity's remaining Kingfisher floatplane observed two shadowing U-boats and two of Empire Shackleton's lifeboats. Fidelity launched LCV-752 and LCV-754 to bring in the lifeboats, and recovered the Kingfisher and the two landing craft with Empire Shackleton's survivors during that afternoon, and launched MTB-105 for anti-submarine patrols through the night. U-615 launched four torpedoes against Fidelity at about 20.00, but the anti-torpedo net protected the ship from damage. MTB-105 experienced engine problems and lost contact with Fidelity at about 23.00, heard radio calls from Fidelity shortly after dawn, but had inadequate battery power to respond. U-435 torpedoed Fidelity at 16.30 and was surprised by the size of the resulting explosion and the great number of men subsequently seen in the water where the ship had sunk. MTB-105 rigged a makeshift sail in an effort to reach land.

Battleford, Shediac, Milne and Meteor broke away on 30 December to refuel in the Azores islands group. With only four escorts remaining and as many as 12 U-boats in contact with the convoy, St Laurent's captain, as commander of Escort Group C1, suffered a nervous breakdown at the scale of the losses. Following the loss of the convoy commodore, he invited two fast British ships with large passenger complements (the 7,206-ton Calgary and 7,905-ton Adrastus) to escape if they found an opportunity. The Canadian destroyer St Francis and British destroyer Viceroy reinforced the convoy escort before the fall of night on 30 December, and the U-boats were ordered to disengage at this time.

Shediac and Meteor exhausted all their fuel before reaching the Azores islands group, the former being towed the last 40 miles (65 km) by Battleford, and Meteor was towed the last 5 miles (8 km) by Milne. All four ships then refuelled and joined the search for survivors. The Canadian corvette Prescott found and rescued the eight men aboard MTB-105 on 1 January, but with the exception of the two-man Kingfisher crew rescued earlier by St Laurent there were no other survivors from Fidelity's crew of 325 and the men rescued from Empire Shackleton. Prescott also saved 26 men from President Francoui, but the recovery effort found no other convoy survivors.

The convoy’s surviving ships reached New York City on 12 January 1943.

The ON.166 convoy of 63 ships departed Liverpool 11 February 1943 and was joined on the following day by the US Escort Group A3 (US Coast Guard cutters Campbell and Spencer, British corvette Dianthus, and Canadian corvettes Chilliwack, Dauphin, Rosthern and Trillium). On 20 February U-604 sighted and reported the convoy after it had become scattered by an eight-day north-westerly gale. Oberleutnant Eberhard Hüttemann’s
U-332 torpedoed the straggling 5,964-ton Norwegian freighter Stigstad on the morning of 21 February. Oberleutnant Hermann Schrüder’s U-623 was sunk by a Consolidated Liberator long-range maritime patrol bomber of the RAF’s No. 120 Squadron during the afternoon of the same day, and Campbell attacked a U-boat that evening, and while post-war analysis concluding that she had sunk Leimkühler’s U-225, more recent re-evaluation indicating that her victim was possibly Korvettenkapitän Georg-Werner Fraatz’s U-529. Kapitänleutnant Adolf Oelrich’s U-92 torpedoed the 9,990-ton British freighter Empire Trader at 20.32 and the 9,348-ton Norwegian freighter N. T. Nielsen Alonso at 01.53 on the night of 21/22 February. Each ship was hit by a single torpedo on the port side, flooding the forward hold and boiler room respectively. The Free Polish destroyer Burza, part of the escort of the following ONS.167 convoy, was then ordered to reinforce the ON.166 convoy’s escort.

Kapitänleutnant Dietrich von der Esch’s U-606 torpedoed the 6,615-ton British freighter Empire Redshank, 5,687-ton US freighter Chattanooga City and 4,959-ton US freighter Expositor after the fall of night on 22 February, but was itself damaged by depth charges from the recently arrived Burza. Campbell was disabled in a collision with U-606, and 12 men were rescued from the crew of the sinking U-boat. Burza left the convoy to tow Campbell back to port. The 1,683-ton British convoy rescue ship Stockport was sunk by Kapitänleutnant Horst Höltring U-604 while returning to the convoy after rescuing men from the three ships torpedoed by U-606. Hasenschar’s U-628 torpedoed the 6,907-ton Panamanian freighter Winkler at 04.20 and the 6,402-ton Norwegian replenishment oiler Glittre at 04.25. Kapitänleutnant Siegfried Hesemann’s U-186 torpedoed the 5,401-ton US freighter Hastings at about 04.30 and the 6,207-ton British freighter Eulima at 04.58 on 23 February, while Spencer, Rosthern and Chilliwack remained with the convoy and Dianthus detached to refuel. Korvettenkapitän Bernhard Zurmühlen’s U-600 torpedoed the 4,391-ton Norwegian freighter Ingria at 05.20 on 24 February, and Kapitänleutnant Gerhard Feiler’s U-653 torpedoed the straggling 7,176-ton US freighter Jonathan Sturges. Hasenschar’s U-628 scored on the 7,264-ton British freighter Manchester Merchant with two torpedoes on the starboard side at 05.27 on 25 February.

The U-boats discontinued their assault on the convoy during 26 February, and the surviving ships were joined by the 9,891-ton British freighter Empire Cavalier from Halifax, Nova Scotia, on 28 February with together with the Canadian corvettes New Westminster, Blairmore and Rimouski, and reached New York City on 3 March 1943.