Convoy ONS 5
Part of TheBattle of the Atlantic of theSecond World War
Relief location map of the North Atlantic Ocean
Date 29 April – 6 May 1943 Location North Atlantic Result British Victory
Belligerents
Germany	United Kingdom  Canada
Commanders and leaders
Karl Dönitz	Convoy: J. K. Brook Escort B7: Peter Gretton
Strength
Star 16 U-Boats Finke 27 U-boats	42 ships 7 escorts
Casualties and losses
7 U-boats sunk 7 U-boats damaged	13 ships sunk [63,000 gross register tons (GRT)]

ONS 5 was the 5th of the numberedON/ONS convoys ofSlow tradeconvoysOutbound from the British Isles toNorth America. TheNorth Atlantic battle around it in May 1943 is regarded as the turning point of theBattle of the Atlantic in World War II. The battle ebbed and flowed over a week and involved more than 50 Allied ships and their escorts, against more than 30U-boats. It saw severe losses on both sides and was almost the last Allied convoy to do so. Losses inflicted on the U-boats became a besetting feature of the campaign. It is seen as the point when the tactical and strategic advantage passed to theAllies, ushering in the period known to theKriegsmarine asBlack May.

Convoy ONS 5 consisted of 43 ships bound fromLiverpool toHalifax. The ships were either in ballast or carrying trade and export goods.^[1] The convoy departed Liverpool on 21 April 1943, and would arrive in Halifax three weeks later on 12 May. The Convoy Commodore was J.K. Brook RNR, travelling in the Norwegian freighterRena.^[2] The escort was provided byMid-Ocean Escort Force groupB7 (CaptainPeter Gretton) comprisingHMS Duncan thedestroyerVidette, frigateTay, andcorvettesSunflower,HMS Snowflake,Loosestrife andPink. The group also contained 2 trawlers,Northern Gem andNorthern Spray as rescue ships, and the fleet oilerBritish Lady for re-fuelling. The convoy was joined by other escort vessels as the battle progressed. Convoy ONS 5 was one of several Allied convoys at sea at the end of April; also in the Western Approaches were Convoy ON 180, just leaving, and Convoy HX 234, just arriving. Approaching the Americas were Convoy ONS 4 and Convoy ON 179; departing was Convoy SC 128, while in mid-Atlantic, due to pass Convoy ONS 5 east of Greenland, was Convoy SC 127. Two other eastbound convoys, Convoy HX 235 and Convoy HX 236, were also in mid-Atlantic, following a southerly route; over 350 ships were in the north Atlantic.

Ranged against the convoy were 58 U-boats in 3 patrol lines,gruppe Specht (Woodpecker) with 17 boats south ofGreenland on the western side of theAir Gap,gruppe Meise (Blue Tit) with 30 boats east of Greenland covering the northern route, andgruppe Amsel (Blackbird) with 11 boats, south ofMeise covering the southern route.Meise had been assembled to catch Convoy SC 127, which had been identified byB-Dienst, but on 26 April the convoy had slipped through a gap in the line and escaped undetected. On 27 April, BdU re-organisedgruppe Meise and the boats furthest east formed a newgruppe Star (Starling), of sixteen U-boats, in a north–south line (a rake) at 30°W between latitudes 61°50′ and 57°00′N, roughly 420 nmi (780 km; 480 mi) east of Greenland. The boats were to be ready by the morning of 28 April to intercept the next ON convoy on the eight-day cycle and the northern end of the line was adjacent to the track of Convoy ONS 5. In the morning of 28 April the convoy was at 61°45′N, 29°11′W, turning onto a south-westerly heading. By the morning of 29 April it would pass through 30°W to 34°51′W.^[3]

Convoy 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.WolfpacksStar andFinke comprised 43 U-boats altogether (though again, not all had been in contact throughout); 6 of these were lost.

Merchant ships departing Liverpool on 21 April 1943 were met byEscort Group B7 at 2:00 p.m. on 22 April and the convoy formed up in high winds and a heavy sea. At 10:00 p.m., the Polish freighterModlin had to turn back with engine trouble. Station-keeping for the remaining ships became increasingly difficult as weather worsened on 23 April.^[4]

At 4:55 p.m. in a moderate gale,B-17 C of206 Squadron, fromBenbecula, dropped six depth charges on the swirl of a diving U-boat. B-17 D foundU-710 on the surface less than an hour later and sank it with depth charges as the U-boat attempted to fight back rather than submerge.U-710 was just 10 nmi (19 km; 12 mi) ahead of the convoy, though probably unaware of its proximity.^[5]

FreightersBornholm andBerkel collided on the evening of 25 April as a moderate west-northwest gale reduced convoy speed to two or three knots.Bornholm began taking on water and left the convoy the next day forIceland.Vidette joined the convoy with three merchant ships from Iceland on 26 April while rescue trawlerNorthern Spray was standing by the straggling freighterPenhale until the straggler was ordered intoReykjavík so the trawler could rejoin the convoy. At noon on 26 April,BdU changed theEnigma machine cypher being used to transmit instructions to the U-boats. Allied intelligence services were unable to decrypt message traffic until the afternoon of 5 May.^[6] The weather moderated enough forDuncan,Vidette andLoosestrife to refuel from the escort oilerBritish Lady on 27 April and a salvage tug from Iceland rescuedBornholm that evening.^[7]

On 28 April, Convoy ONS 5 arrived at theStar patrol area and was sighted at 9:00 a.m. byU-650, that held contact despite being forced to dive to avoid approaching aircraft at 10:14 a.m., 11:50 a.m. and 3:18 p.m. By nightfallU-650 had been joined byU-375,U-386,U-528 andU-537. The U-boats' contact reports alerted Gretton to the presence of U-boats on the convoy's portbow,beam,quarter andastern.Duncan andTay made an unsuccessful depth charge attack after sighting a U-boat on the port bow at 6:30 p.m.^[8]

Gretton mounted a vigorous defence as the U-boats attacked after dark. At 8:00 p.m.Sunflower gained aradar contact at 3,800 yd (1.9 nmi), on closing lost the radar contact, gained a doubtfulASDIC contact, and dropped two depth charges. At 10:45 p.m.Duncan detected a radar contact at 3,500 yd (1.7 nmi) and upon closing lost the radar contact, gained an ASDIC contact at 1,500 yd (0.74 nmi) , lost contact at 1,100 yd (0.54 nmi) and dropped one depth charge. Upon returning to stationDuncan got a radar contact at 2,300 yd (1.1 nmi) and upon closing sighted a U-boat which dived at 1,100 yd (0.54 nmi) and appeared on ASDIC at 500 yards (0.25 nmi).Duncan dropped a pattern of ten depth charges and while turning for another attack, gained another radar contact. The radar contact disappeared at a range of 3,000 yd (1.5 nmi).Duncan made no ASDIC contact, but dropped a depth charge at the estimated diving position before making another radar contact at 4,000 yd (2.0 nmi). AsDuncan closed, the U-boat dived at a range of 1,500 yd (0.74 nmi).Duncan gained a good ASDIC contact and dropped a pattern of ten depth charges over a visible wake. Two more depth charges were dropped when a weak ASDIC contact was regained at 12:45 a.m.

At 1:32 a.m.Snowflake approached a hydrophone contact, andU-532 was detected visually and on radar at a range of 1,300 yd (0.64 nmi).U-532 launched six torpedoes. The closest one missedSnowflake by about 20 yd (18 m). AfterU-532 dived,Snowflake dropped three depth charges on the initial ASDIC contact and ten depth charges when contact was regained at 2,000 yd (0.99 nmi).Snowflake regained ASDIC contact at 1,400 yd (0.69 nmi) and dropped another pattern of ten depth charges. A short time laterTay dropped depth charges on a good ASDIC contact astern of the convoy.^[9]U-532 returned to base to repair depth charge damage.U-386 andU-528 were also damaged by these attacks and forced to return to base.U-386 arrived atSt Nazaire on 11 May butU-528 was attacked in theBay of Biscay and sunk by aircraft on the same day.^[10]

U-258 andU-650 maintained contact through the night andU-258 was submerged ahead of the convoy at dawn on 29 April. As the convoy passed overhead at 5:30 a.m.,U-258 rose to periscope depth and launched two torpedoes atMcKeesport. After one torpedo hitMcKeesport on the starboard bow,Northern Gem detectedU-258 and dropped three depth charges.Snowflake dropped a depth charge on a doubtful Asdic contact at 6:05 a.m. and two more depth charges at 6:15 a.m. after contact was regained at a range of 1,200 yd (0.59 nmi).McKeesport was abandoned,Northern Gem rescued all but one of the crew and it was scuttled by the escort.^[11]U-258 had also been damaged and was forced to return to base.

The Admiralty arranged reinforcements for Convoy ONS 5.HMS Oribi was detached fromConvoy SC127 and the destroyersPenn,Panther,Impulsive andOffa, of the 3rd Support Group (Capt. J. M. McCoy) sailed from Newfoundland. The weather rapidly deteriorated and the convoy was sailing into a full gale by late afternoon of 29 April. About 5:00 p.m.Sunflower was struck by a wave which filled thecrow's nest with water.Oribi was slowed to 11 kn (20 km/h; 13 mph) by the storm, but joined the convoy at 11:00 p.m. asTay was attacking a U-boat astern. At 11:12 p.m.Duncan obtained an ASDIC contact at 1,100 yd (0.54 nmi)Duncan andSnowflake dropped depth charges to discourage the U-boats.^[11]

The convoy found itself making less than 3 kn (5.6 km/h; 3.5 mph) headway into a Force 10 gale. The convoy started to be scattered, some ships ending up 30 nmi (56 km; 35 mi) from the convoy, and the escorts were kept busy rounding up stragglers.Oribi was able to refuel from the convoy oiler when the storm abated briefly on 30 April before the weather again made re-fuelling impossible, and a number of the destroyers became low on fuel, throwing doubt on whether they could continue. At 11:05 p.m.Snowflake made a radar contact at 3,300 yd (1.6 nmi) and dropped a depth charge after the U-boat dived when illuminated bystar shell. The escorts dropped some random depth charges until dawn and Admiral Dönitz cancelled the chase on the evening of 1 May.^[12]

On 1 May Dönitz ordered boats fromStar andSpecht, 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 to intercept the westbound Convoy SC 128. The 3rd Support Group destroyers joined the convoy at 1:00 a.m. 2 May, but the fuel situation aboard destroyers became increasingly desperate as weather and frequent course adjustments to avoid icebergs prevented refuelling. At 2:00 p.m. on 3 May Gretton was forced to takeDuncan toSt John's at economical speed [8 kn (15 km/h; 9.2 mph)] and he arrived with only 4 per cent of the fuel remaining. Command was assumed by Lt-Cdr R.E. Sherwood, of HMSTay. The Asdic set aboardTay failed just as Sherwood took over.Impulsive also detached to Iceland at 7:00 p.m. on 3 May, withNorthern Gem carrying the survivors fromMcKeesport, whilePenn andPanther detached for Newfoundland at 6:00 a.m. on 4 May.^[13]

By 4 May the weather had abated to Force 6, and the convoy was making up to 6 kn (11 km/h; 6.9 mph), though reduced to 30 ships and 7 escorts.The rest were scattered and proceeding independently, including a group of four withPink, trailing 80 nmi (150 km; 92 mi) behind the main body. The 1st Support Group sailed from Newfoundland at noon with the frigatesWear,Jed,Spey and the sloopsPelican andSennen to replaceOribi andOffa whose fuel state would become dangerously low on 5 May.U-628 of groupFinke, assembled to catch Convoy SC 128, sighted Convoy ONS 5 at 8:18 p.m. Two of the gathering groupFinke U-boats were attacked by RCAFCansos. One U-boat, thought to have beenU-630 was sunk but is now believed to have beenU-209, which was damaged in an attack by Canso W and foundered later while attempting to return to base. The other,U-438, was only slightly damaged in attacks by Canso E.^[14]

At 10:20 p.m.Vidette detectedU-514 on radar at 3,600 yd (1.8 nmi) and approached untilU-514 dived when the range dropped to 900 yd (0.44 nmi).Vidette a pattern of 14 depth charges causing damage that putU-514 out of the battle until 7 May.North Britain was straggling 6 nmi (11 km; 6.9 mi) astern of the convoy and sank within two minutes of being torpedoed byU-707 at 10:37 p.m.Vidette detectedU-662 on radar at 3,600 yd (1.8 nmi) and upon closing, sightedU-732 at 1,000 yd (0.49 nmi) . The conning tower was still visible at 80 yd (73 m) and a pattern of 14 depth charges dropped by eye caused damage requiringU-732 to return to base.

U-264 andU-628 each launched five torpedoes shortly after midnight.Harbury was hit at 12:46 a.m.;Harperly was hit by two torpedoes at 1:04 a.m. andWest Maximus was hit by a torpedo at 1:03 a.m., another at 1:10 a.m. and a third at 1:35 a.m. Both U-boats claimed three ships; but modern historians credit the first freighter toU-628 and the other two toU-264.^[15] One of the torpedoes passed within 125 yd (114 m) ofSnowflake. At 1:22 a.m.Snowflake started closing a radar contact illuminated by star shells fired byOribi; and both ships dropped depth charges. The gunfire encouragedU-264 to dive and the depth charges forcedU-270 to return to base.^[16]U-358 torpedoedBristol City at 2:25 a.m. andWentworth at 2:30 a.m.^[17] At dawn,Lorient was missing from the convoy. No witnesses to her destruction survived the battle. BeforeU-125 was sunk, she sent a radio report about sinking a steamship sailing independently and historians assumeLorient straggled from the convoy and was torpedoed byU-125.^[18]

Northern Spray picked up 143 survivors fromNorth Britain,Harbury,Harperly andWest Maximus by 7:00 a.m. and was detached to take the rescued men to Newfoundland.Loosestrife assumed the role of rescue ship and picked up the survivors fromBristol City andWentworth. At 10:57 a.m.Oribi sighted a surfaced U-boat at 7 nmi (13 km; 8.1 mi).U-223,U-231,U-621 andU-634 dived asOribi approached.^[19]Oribi dropped 14 depth charges andU-638 torpedoedDolius at 12:40 p.m.Sunflower gained an ASDIC contact at 1,200 yd (0.59 nmi) within minutes and destroyedU-638 with a pattern of ten depth charges, before rescuing survivors fromDolius.^[20]Tay,Oribi, andOffa refuelled from convoy oilers that afternoon.^[21]Selvistan,Gharinda andBonde were hit by a salvo of four torpedoes fromU-266 within the space of a few minutes about 7:50 p.m.Selvistan andBonde sank within two minutes.Tay rescued survivors from the ships whileOffa made depth charge attacks, damagingU-266, which was sunk by aircraft on 15 May while attempting to reach base for repairs.^[22]

At midday,Pink (LieutenantRobert Atkinson) made a firm ASDIC contact 2,200 yd (1.1 nmi) ahead of her small convoy, still proceeding separately.Pink spent 90 minutes making five depth charge andhedgehog attacks.Pink received post-war credit for destruction ofU-192 but later analysis concluded that the victim,U-358, returned to base after being damaged.U-584 torpedoedWest Madaket whilePink was attackingU-358 andPink rescued the survivors.^[23]

As dark fell on 5 May,Tay counted seven U-boats surfaced in the convoy's path but Convoy ONS 5 was entering the fog formed where the warmGulf Stream meets the coldLabrador Current off theGrand Banks of Newfoundland. Visibility dropped to 1 nmi (1.9 km; 1.2 mi) by 10:02 p.m. and to 100 yd (91 m) by 1:00 a.m. Britishcentimetric radar enabled the escorts to see while the U-boats could not. Many of the U-boats involved never returned to base and historians struggle to correlate reports of the dozens of ships interacting briefly in no fewer than 24 attempted attacks.^[24] At 11:09 p.m.Vidette made a radar contact at 5,100 yd (2.5 nmi) and a second appeared while closing the first.Vidette dropped a pattern of ten depth charges on a submarine seen submerging 700 yd (0.35 nmi) ahead, and then moved on to drop a pattern of five depth charges on the second contact which became visible at 900 yd (0.44 nmi). Historians suggest the first attack destroyedU-531.^[25]

At 0:30 a.m.Loosestrife made a radar contact at 5,200 yd (2.6 nmi). The U-boat turned away when the range reached 500 yd (460 m) and fired two torpedoes atLoosestrife from its stern tubes while diving.Loosestrife dropped a pattern of ten depth charges as it overran the diving U-boat. A reported slick of oil and debris is believed to have been produced by the destruction ofU-192.^[26] At 2:52 a.m.Oribi collided withU-125 first seen at a range of 200 yd (180 m) while investigating an ASDIC contact, but lost contact after the collision. While pursuing an ASDIC contact,Snowflake detectedU-125 on radar at 3:54 a.m., observed heavy conning tower damage by searchlight at a range of 100 yd (91 m), and watched the crew detonate scuttling charges and abandon ship. The escorts continued their protective patrolling around the convoy rather than attempt to rescue of the U-boat crew assumed to have sunkLorient.^[27]

At 4:06 a.m.Vidette made an ASDIC contact at 800 yd (730 m), and made a hedgehog attack causing two explosions. Historians suggest this attack destroyedU-630 At 4:43 a.m.Sunflower made an ASDIC contact at 1,200 yd (0.59 nmi) and subsequently sighted a surfacing U-boat.Sunflower rammedU-533 and dropped two depth charges asU-533 attempted to dive.Loosestrife andU-533 were able to make repairs and remain at sea.^[28] At 5:52 a.m.Pelican was leading the 1st Support Group to reinforce the convoy escort when it detected a radar contact at 5,300 yd (2.6 nmi).Pelican made visual contact at 300 yd (270 m), dropped a pattern of ten depth charges where the U-boat dived and dropped a second pattern of nine depth charges after regaining contact. Historians suggest these attacks destroyedU-438.^[29]Finke had already outlasted its usefulness and faced mounting losses if the attack continued. Realising his mistake, Dönitz called off the assault on 6 May and orderedFinke to retire.

Convoy ONS 5 had been attacked by over 40 U-boats. With the loss of 13 ships totalling 63,000 GRT, the escorts had inflicted a loss of 6 U-boats and serious damage on 7 more. The convoy escorts had mastered the art of convoy protection; the weapons and expertise at their disposal meant that henceforth they would be able to protect their charges, repel attack and to inflict significant losses on the attacker. Convoy ONS 5 marked the turning point in the battle of the Atlantic. Following this action, the Allies inflicted defeats on theU-boat Arm known asBlack May. This culminated in Dönitz withdrawing the U-boats from the North Atlantic. The naval official historian,Stephen Roskill wrote,

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 theQuiberon Bay orthe Nile.^[30]

Ships sunk in Convoy ONS 5^[31]

Date	Name	Year	GRT	Flag	Notes
29 April 1943	McKeesport	1919	6,198	United States	U-258, 61°22′N, 30°20′W, 1† 67 surv, scuttledHMS Tay
5 May 1943	Lorient	1921	4,185	United Kingdom	U-125, 54°N, 44°W, 46 casualties
4 May 1943	North Britain	1940	4,635	United Kingdom	U-707, 55°08′N, 42°43′W 34† 12 surv
5 May 1943	Harbury	1934	5,081	United Kingdom	U-628,U-364 55°01′N, 42°59′W, 7† 43 surv
5 May 1943	West Maximus	1919	5,561	United States	U-264, 55°10′N, 43°W, 5† 57 surv
5 May 1943	Harperley	1930	4,586	United Kingdom	U-264, 55°N, 42°58′W, 11† 38 surv
5 May 1943	Bristol City	1920	2,864	United Kingdom	U-358, 54°N, 43°55′W, 15† 29 surv
5 May 1943	Wentworth	1919	5,212	United Kingdom	U-358,U-628, 53°59′N, 43°55′W, 5† 42 surv
5 May 1943	Dolius	1924	5,507	United Kingdom	U-638, 54°N, 43°35′W, 4† 68 surv
5 May 1943	West Madaket	1918	5,565	United States	U-584, 54°47′N, 45°12′W, 0† 61 surv, scuttledHMS Pink
5 May 1943	Selvistan	1924	5,136	United Kingdom	U-266, 6† 40 surv
5 May 1943	Gharinda	1919	5,306	United Kingdom	U-266, 53°10′N, 44°40′W, 0† 92 surv
5 May 1943	Bonde	1936	1,570	Norway	U-266, 53°28′N, 44°20′W, 14† 12 surv

• Convoy Battles of World War II

• Blair, Clay (2000) [1998].Hitler's U-Boat War: The Hunted 1942–1945. Vol. II (pbk. repr. ed.). London: Cassell.ISBN 0-304-35261-6.
• Gretton, Peter (1964).Convoy Escort Commander. London: Cassell.OCLC 6441688.
• Hague, Arnold (2000).The Allied Convoy System 1939–1945, Its Organisation, Defence and Operation. London: Chatham.ISBN 1-86176-147-3.
• Kemp, Paul (1997).U-Boats Destroyed, German Submarine losses in the World Wars. London: Arms and Armour.ISBN 1-85409-515-3.
• Milner, Marc (2018) [1985].North Atlantic Run: The Royal Canadian Navy and the Battle for the Convoys. Toronto: University of Toronto Press.ISBN 978-1-4875-7728-5.
• Milner, Marc (2011) [2003].Battle of the Atlantic. Stroud: Spellmount (History Press).ISBN 978-0-7524-6646-0.
• Rohwer, Jürgen; Hümmelchen, Gerhard (2005) [1972].Chronology of the War at Sea, 1939–1945: The Naval History of World War Two (3rd rev. ed.). London: Chatham.ISBN 978-1-86176-257-3.
• Sharpe, Peter (1998).U-Boat Fact File. Leicester: Midland Publishing.ISBN 1-85780-072-9.
• Vat, Dan van der (1988).The Atlantic Campaign. London: Hodder & Stoughton.ISBN 0-340-37751-8.
• Woodman, Richard (2005) [2004].The Real Cruel Sea: The Merchant Navy in the Battle of the Atlantic, 1939–1943 (Pbk. ed.). London: John Murray.ISBN 0-7195-6599-5.

• ONS 5 at convoyweb
• Convoy ONS 5 at warsailors
• ONS 5 - 28 Apr 1943 – 6 May 1943
• Timeline of Battle of the Atlantic 1943-45

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