Convoy ONS 5

Convoy ONS 5
Convoy ONS 5
Part of World War II
Date 29 April-6 May 1943
Location North Atlantic
Result British Victory
War Ensign of Germany 1938-1945.svg Germany Naval Ensign of the United Kingdom.svg United Kingdom
Commanders and leaders
Admiral Karl Dönitz Convoy Comm: JK Brook RNR
Escort B7: Cdr Peter Gretton
Star 16 U-Boats
Finke 27 U-boats
42 ships
7 escorts
Casualties and losses
6 U-boats sunk
7 U-boats damaged
13 ships sunk (63,000 gross register tons (GRT))

ONS 5 was a North Atlantic convoy during the battle of the Atlantic in World War II; the battle surrounding it in May 1943 is regarded as the turning point of the Atlantic campaign. The battle ebbed and flowed over a period of a week, and involved more than 50 Allied ships and their escorts, and over 30 U-boats. It saw heavy losses on both sides. However it was almost the last Allied convoy to do so, while losses inflicted on attacking U-boats and U-boat groups became a besetting feature of the campaign; As such it is seen as the point when the tactical and strategic advantage passed to the Allies, and ushered in the period known to the German Navy as Black May.


The Protagonists

ONS 5 was a slow west-bound convoy of the ONS series organized and run during the Atlantic campaign. It consisted of 42 ships bound from Liverpool to Halifax, the ships either in ballast or carrying trade and export goods. The convoy departed Liverpool on 21 April 1943, and would arrive in Halifax three weeks later on 12 May. It was under the command of JK Brook RNR as Convoy Commodore, travelling in the Norwegian freighter Rena. The escort was provided by Mid-Ocean Escort Force group B7, 7 warships under Captain Peter Gretton, in the destroyer Duncan. Also in the group were the destroyer Vidette, frigate Tay, and corvettes Sunflower, Snowflake, Loosestrife, and Pink. The group also contained 2 trawlers, Northern Gem and Northern Spray as rescue ships, and the fleet oiler British Lady for mid-ocean re-fuelling. The convoy was joined by other escort vessels as the battle progressed.

ONS 5 was just one of the allied convoys at sea at the end of April; also in the Western Approaches were ON 180, just leaving, and HX 234, just arriving. Approaching the Americas were ONS 4 and ON 179; departing was SC 128, while in mid-Atlantic, due to pass ONS 5 east of Greenland, was SC 127. Two other east-bound convoys, HX 235 and HX 236, were also in mid-Atlantic, following a southerly route. This accounted for over 350 ships on the move in the north Atlantic at that time.

Ranged against them were 58 U-boats in 3 patrol lines; Specht (Woodpecker) with 17 boats south of Greenland on the western side of the Air Gap; Meise (Bluetit) with 30 boats east of Greenland covering the northern route, and Amsel (Blackbird) with 11 boats, south of Meise covering the southern route.

Meise had been deployed to catch SC 127, which had been identified by B-Deinst, but on 26 April SC 127 had slipped through a gap in the line and escaped undetected. Realizing what had happened on 27 April,, and aware that a slow west-bound convoy was imminent, Meise was re-configured; the easternmost boats (16 in all) formed the patrol line Star (Starling) to intercept it. At 8am on 28 April U-650 sighted ONS 5, and group Star quickly gathered for the attack.

The Action

The convoy departed Liverpool on 21 April 1943, and was quickly involved in incident. On the first night, the freighter Modlin had to turn back with engine trouble. On the 24th, in a moderate gale, the air escort from Scotland, spotted and sank U-710 which was just 10 miles ahead of the convoy, though probably unaware of its proximity.

On 26th the freighter Penhale was storm-damaged, and detached to return to Reykjavík escorted by Northern Gem, which re-joined the following day. Also on the same day Vidette joined with 3 merchant ships from Iceland.

The first battle

On the 28th ONS 5 arrived at the Star patrol area, and was sighted by U-650. By nightfall she had been joined by 4 others ( U-375, U-386, U-528 and U-537), and at midnight they began their attack.

Warned by the radio chatter of their presence, Gretton mounted a vigorous defence; in the course of the night none of the ships were hit, while 2 of the U-boats, U-386 and U-532, were damaged and forced to return to base. (U-386 arrived safely at St Nazaire on 11 May, but U-532 was attacked in the Bay of Biscay and sunk by aircraft on the same day). The assault continued into the day; at midday on the 29th one ship, McKeesport, was torpedoed and sunk. The attacker, U-258, was also damaged in the affair, and was also forced to return to base.

Also on 29th the Admiralty arranged reinforcements for ONS 5; HMS Oribi, detached from SC127 would arrive on the 30th, while 3rd Support Group, (the 4 destroyers Penn, Panther, Impulsive and Offa,under Capt. JA McCoy RN) would arrive on 1 May.

The storm

Over the next few days the action was dictated by the weather. In worsening conditions ONS 5 found itself making less than 3 knots headway into a Force 10 gale. The convoy started to be scattered, some ships ending up 30 miles from the convoy, and the escorts were kept busy rounding up stragglers. On 30th, and 1st reinforcements arrived, making the escorts' task easier. The weather made re-fuelling impossible, and a number of the destroyers became so low on fuel as to throw doubt on whether they could continue. On 3rd Gretton was forced to take Duncan to St John's at economical speed (8 knots); he arrived there with just hours to spare. In Gretton's absence command was assumed by Lt-Cdr RE Sherwood, of HMS Tay.

Later that night Impulsive also detached to Iceland, with Northern Gem carrying the survivors from McKeesport, while Penn and Panther detached for Newfoundland.

Meanwhile the U-boats tried to maintain contact, though any attack was impossible. Only 6 of the Star boats had been able to make contact;of these 3 had been forced to return to base. Donitz decided that nothing could further be gained and on 1 May ordered boats from Star and Specht, with some newcomers to form a new patrol line to the west. This was group Finke (Finch) which was in place on 3 May numbering 27 boats, and tasked with intercepting westbound convoy SC128. This reorganization was also not without incident; on 1 May two of the newcomers were attacked by air patrol in separate incidents while joining Finke. One was thought to have been U-630, and sunk; but is now believed to have been U-209, which was damaged in the attack, succumbing later while attempting to return to base. The other, U-438, was only slightly damaged in the attack.

The second battle

By 4 May the weather had abated to Force 6, and ONS 5 was now making up to 6 knots, though reduced to 30 ships and 7 escorts. The rest were scattered and proceeding independently, including a group of 4 with Pink, trailing some 80 miles behind the main body. On 4 May at local midday ships were sighted by U-628 of group Finke; not SC128, as they were expecting, but ONS 5. The boats of Finke started to gather, and by evening were ready to make their attack. The assault started at nightfall and continued throughout the night; under the relentless pressure 5 ships were torpedoed while a number of U-boats were damaged.

The assault continued into the day, the U-boats switching to submerged attacks, and a further 4 ships were lost. Several boats also found Pink’s party and made an attack; one ship, West Makadet, was sunk, while Pink mounted a spirited attack on a contact, and was credited with the destruction of U-192, though the recipient was more likely to have been U-358, which was damaged.

Determined to see results, Donitz ordered the assault to continue into the night; however with a thick fog forming, the advantage passed to the escorts. The U-boats lost visibility in the fog, while the escorts, equipped with radar, were able to strike un-hindered. The assault was repulsed; no ships were lost, but 3 U-boats, (U-638, U-125 and U-531) were sunk.

On the morning of 6 May, reinforcement in the form of 1st Support Group arrived. Led by Cdr GN Brewer in HMS Pelican, they announced their arrival by attacking and sinking U-438; while the cutter Sennen, sent to help Pink’s party, made an attack which was also credited as a kill, but was later found to have been unsuccessful. With the other members of 1st Support Group, the frigates Jed, Wear and Spey, the escort now stood at 13 warships.

Finke had already outlasted its usefulness, and faced mounting losses if the attack continued. Realizing his mistake, Donitz called off the assault on 6 May and ordered Finke to retire.

Although not home for another week, ONS 5 was not attacked again; this was as well, for Offa and Oribi detached on 6th through lack of fuel, while the ships of B7 group, low on fuel and ammunition, were in little shape for more action. Only the ships of 1st Support Group were in any state to fight.


In the course of a week, ONS 5 had been the subject of attacks by a force of over 40 U-boats. With the loss of 13 ships totalling 63,000 tons, the escorts had inflicted the loss of 6 U-boats, and serious damage on 7 more.

This battle demonstrated that the convoy escorts had mastered the art of convoy protection; the weapon and expertise at their disposal meant that henceforth they would be able not only be able to protect their charges and repel attack, but they would also be able to inflict significant losses on the attacker.

ONS 5 marked the turning point in the battle of the Atlantic. Following this action, the Allies inflicted a series of defeats and heavy losses on the U-boat Arm, a period known as Black May. This culminated in Donitz withdrawing his forces from the North Atlantic arena.

The official historian, Stephen Roskill commented: “This seven day battle, fought against thirty U-boats, is marked only by latitude and longitude, and has no name by which it will be remembered; but it was, in its own way, as decisive as Quiberon Bay or the Nile”.[1],[2],


Allied ships lost

Date Name Nationality Casualties Tonnage Sunk by…
29 April 1943 McKeesport US 11 6198 GRT U-258
4/5 May Lorient British  ? 4737 GRT U-125
4/5 North Britain British  ? 4635 GRT U-707
4/5 Harbury British 7 5081 GRT U-628
4/5 West Maximus US 5 5561 GRT U-264
4/5 Harpurley British 11 4586 GRT U-264
4/5 Bristol City British 15 2864 GRT U-358
4/5 Wentworth British 5 May 5512 GRT U-358
5 Dolius British 4 5507 GRT U-638
5 West Makadet US nil 5565 GRT U-584
5/6 May Selvistan British 6 5136 GRT U-266
5/6 Gharinda British nil 5306 GRT U-266
5/6 Bonde Norwegian 5 1570 GRT U-266

U-boats lost

Date Number Type Captain Casualties Sunk by…
4.5.43 U-630 VIIC Wachter 47 Canso 5 Sqdn RCAF
5/6 U-638 VIIC Straudinger 44 Loosestrife
5/6 U-125 IXC Folkers 54 Oribi, Snowflake
5/6 U-531 IXC/40 Neckel 54 Vidette
 ?5.5.43 U-192 IXC/40 Happe 55 Pink
6.5.43 U-438 VIIC Hensohn 48 Pelican

Ships involved

ONS 5 comprised 42 ships and 16 escorts, (though not all were present at the same time); 13 ships were lost in the course of the 7 day engagement.

Wolfpacks Star and Finke comprised 43 U-boats (though again, not all had been in contact throughout); 6 of these were lost.


  1. ^ Roskill, p. 375.
  2. ^ Gannon, p. 239.

External links


  • Arnold Hague : The Allied Convoy System 1939-1945 (2000). ISBN (Canada) 1 55125 033 0 :ISBN (UK) 1 86176 147 3.
  • Peter Gretton : Convoy Escort Commander (1964). ISBN (none)

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