Convoy ONS 5

ONS 5 was the 5th of the numbered ONS series of Slow trade convoys Outbound from the British Isles to North America. The North Atlantic battle surrounding it in May 1943 is regarded as the turning point of the Battle of the Atlantic in World War II.
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 Nazi Germany's "Kriegsmarine" as Black May.
Background.
ONS 5 consisted of 43 ships bound from Liverpool to Halifax. The ships were 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, traveling 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-Dienst, 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.
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.
Action.
Merchant ships departing Liverpool on 21 April 1943 were met by Escort Group B7 at 1400 on the 22nd; and the convoy formed up in high winds and a heavy sea. At 2200, the Polish freighter "Modlin" had to turn back with engine trouble. Station-keeping for the remaining ships became increasingly difficult as weather worsened on the 23rd.
24 April.
At 1655 on the 24th, in a moderate gale, Flying Fortress C of 206 Squadron RAF from Benbecula, dropped six depth charges on the swirl of a diving U-boat. Fortress D found 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 ahead of the convoy, though probably unaware of its proximity.
25–27 April.
Freighters "Bornholm" and "Berkel" collided on the evening of the 25th as a moderate west-northwest gale reduced convoy speed to two or three knots. "Bornholm" began taking on water and left the convoy on the 26th attempting to reach Iceland. "Vidette" joined the convoy with three merchant ships from Iceland on the 26th while rescue trawler "Northern Spray" was standing by the straggling freighter "Penhale" until the straggler was ordered into Reykjavík so the trawler could rejoin the convoy. At noon on the 26th, BdU changed the Enigma 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. The weather moderated enough for "Duncan", "Vidette" and "Loosestrife" to refuel from the escort oiler "British Lady" on the 27th and a salvage tug from Iceland rescued "Bornholm" that evening.
Battle of 28–29 April.
On the 28th ONS 5 arrived at the "Star" patrol area, and was sighted at 0900 by "U-650". "U-650" held contact despite being forced to dive three times to avoid approaching aircraft at 1014, 1150 and 1518. By nightfall "U-650" had been joined by "U-375", "U-386", "U-528" and "U-537". The U-boats' contact reports alerted Commander Gretton to the presence of U-boats on the convoy's port bow, beam, and quarter and astern. "Duncan" and "Tay" made an unsuccessful depth charge attack after sighting a U-boat on the port bow at 1830.
Gretton mounted a vigorous defence as the U-boats attacked after dark. At 2000 "Sunflower" detected a radar contact at ; and upon closing lost the radar contact, gained a doubtful ASDIC contact, and dropped two depth charges. At 2245 "Duncan" detected a radar contact at ; and upon closing lost the radar contact, gained an ASDIC contact at , lost contact at , and dropped one depth charge. Upon returning to station "Duncan" detected a radar contact at ; and upon closing sighted a U-boat which dived at , and appeared on ASDIC at . "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 . "Duncan" made no ASDIC contact, but dropped a single depth charge at the estimated diving position before making another radar contact at . As "Duncan" closed, the U-boat dived at a range of . "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 0045. At 0132 "Snowflake" approached a hydrophone contact, and "U-532" was detected visually and on radar at a range of . "U-532" launched six torpedoes. The closest one missed "Snowflake" by about . After "U-532" dived, "Snowflake" dropped three depth charges on the initial ASDIC contact and ten depth charges when contact was regained at . "Snowflake" regained ASDIC contact at and dropped another pattern of ten depth charges. A short time later "Tay" dropped depth charges on a good ASDIC contact astern of the convoy. "U-532" returned to base to repair depth charge damage. "U-386" and "U-528", were also damaged by these attacks and forced to return to base. "U-386" arrived safely at St Nazaire on 11 May, but "U-528" was attacked in the Bay of Biscay and sunk by aircraft on the same day.
"U-258" and "U-650" maintained contact through the night, and "U-258" was submerged ahead on the convoy at dawn on the 29th. As the convoy passed overhead at 0530, "U-258" rose to periscope depth and launched two torpedoes at "McKeesport". After one torpedo hit "McKeesport" on the starboard bow, "Northern Gem" detected "U-258" and dropped three depth charges. "Snowflake" dropped a single depth charge on a doubtful SONAR contact at 0605 and two more depth charges at 0615 after contact was regained at a range of . "McKeesport" was abandoned and sunk by the escort to prevent discovery of classified documents by German boarders. "Northern Gem" rescued all but one of the crew. "U-258" had also been damaged, and was forced to return to base. The Admiralty arranged reinforcements for ONS 5 in response to this battle. HMS "Oribi" was detached from SC127, and destroyers "Penn", "Panther", "Impulsive", and "Offa", of the 3rd Support Group under Capt. J.M. McCoy, RN, sailed from Newfoundland. Weather rapidly deteriorated, and the convoy was sailing into a full gale by late afternoon of the 29th. About 1700 "Sunflower" was struck by a wave which filled the crow's nest with water. "Oribi" was slowed to 11 knots by the storm, but joined the convoy at 2300 as "Tay" was attacking a U-boat astern. At 2312 "Duncan" obtained an ASDIC contact at ; and both "Duncan" and "Snowflake" dropped depth charges to discourage the U-boats.
30 April.
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. "Oribi" was able to refuel from the convoy oiler when the storm abated briefly on the 30th before the weather again made re-fuelling impossible, and a number of the destroyers became so low on fuel as to throw doubt on whether they could continue. At 2305 "Snowflake" made a radar contact at and dropped a single depth charge after the U-boat dived when illuminated by star shell. The escorts dropped some random depth charges until dawn, and Admiral Dönitz cancelled the chase on the evening of 1 May.
Regrouping 1–3 May.
On 1 May Dönitz 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. The 3rd Support Group destroyers joined the convoy at 0100 2 May, but the fuel situation aboard destroyers became increasingly desperate as weather and frequent course adjustments to avoid icebergs prevented refueling. At 1400 on the 3rd Gretton was forced to take "Duncan" to St John's at economical speed (8 knots); and he arrived there with only 4 percent fuel remaining. In Gretton's absence, command was assumed by Lt-Cdr RE Sherwood, of HMS "Tay". The SONAR set aboard "Tay" failed just as Sherwood assumed command of the escort group. "Impulsive" also detached to Iceland at 1900 3 May, with "Northern Gem" carrying the survivors from "McKeesport", while "Penn" and "Panther" detached for Newfoundland at 0600 4 May.
4 May.
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 four with "Pink", trailing some 80 miles behind the main body. The 1st Support Group sailed from Newfoundland at midday with frigates "Wear", "Jed", "Spey" and sloops "Pelican" and "Sennen" to replace "Oribi" and "Offa" whose fuel state would become critical on the 5th. "U-628" of group "Finke", assembled to catch convoy SC 128, sighted convoy ONS 5 at 2018. Two of the gathering group "Finke" U-boats were attacked by RCAF Cansos in separate incidents. One thought to have been "U-630" was sunk; but is now believed to have been "U-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.
At 2220 "Vidette" detected "U-514" on radar at and approached until "U-514" dived when the range dropped to . "Vidette" punished "U-514" with a pattern of 14 depth charges causing damage putting "U-514" out of the battle until 7 May. "North Britain" was straggling astern of the convoy, and sank within two minutes of being torpedoed by "U-707" at 2237. "Vidette" detected "U-662" on radar at and, upon closing, sighted "U-732" at . The conning tower was still visible at a range of ; and a pattern of 14 depth charges dropped by eye caused damage requiring "U-732" to return to base.
5 May.
"U-264" and "U-628" each launched five torpedoes shortly after midnight. "Harbury" was hit at 0046; "Harperly" was hit by two torpedoes at 0104; and "West Maximus" was hit by one torpedo at 0103, another at 0110, and a third at 0135. Both U-boats claimed three ships; but modern historians credit the first freighter to "U-628" and the other two to "U-264". One of the torpedoes passed within of "Snowflake". At 0122 "Snowflake" started closing a radar contact illuminated by star shells fired by "Oribi"; and both ships dropped depth charges. The gunfire encouraged "U-264" to dive, and the depth charges forced "U-270" to return to base. "U-358" torpedoed "Bristol City" at 0225, and "Wentworth" at 0230. At dawn, "Lorient" was missing from the convoy. No witnesses to her destruction survived the battle. Before "U-125" was sunk, she sent a radio report about sinking a steamship sailing independently; and modern historians assume "Lorient" straggled from the convoy and was torpedoed by "U-125".
"Northern Spray" picked up 143 survivors from "North Britain", "Harbury", "Harperly", and "West Maximus" by 0700 and was detached to take the rescued men to Newfoundland. "Loosestrife" assumed the role of rescue ship and picked up the survivors from "Bristol City" and "Wentworth". At 1057 "Oribi" sighted a surfaced U-boat at . "U-223", "U-231", "U-621", and "U-634" dived as "Oribi" approached. "Oribi" dropped 14 depth charges after the U-boats dived. "U-638" torpedoed "Dolius" at 1240. "Sunflower" gained an ASDIC contact at within minutes and destroyed "U-638" with a pattern of ten depth charges before rescuing survivors from "Dolius". "Tay", "Oribi", and "Offa" refueled from convoy oilers that afternoon. "Selvistan", "Gharinda", and "Bonde" were hit by a salvo of four torpedoes from "U-266" within the space of a few minutes about 1950. "Selvistan" and "Bonde" sank within two minutes. "Tay" rescued survivors from the three ships while "Offa" made depth charge attacks damaging "U-266", which was sunk by aircraft on 15 May while attempting to reach base for repairs.
At midday, "Pink" commanded by Lieutenant Atkinson made a firm ASDIC contact ahead of her small convoy proceeding separately. "Pink" spent 90 minutes making five depth charge and hedgehog attacks. "Pink" received post-war credit for destruction of "U-192"; but later analysis concluded the victim, "U-358", returned to base after being damaged. "U-584" torpedoed "West Makadet" while "Pink" was attacking "U-358". "Pink" rescued the survivors.
Night of 5–6 May.
As May 5 faded into darkness, "Tay" counted seven U-boats surfaced in the convoy's path; but ONS 5 was entering the fog formed where the warm Gulf Stream meets the cold Labrador Current off the Grand Banks of Newfoundland. Visibility dropped to by 2202 and to by 0100. British centimetric radar enabled the escorts to see while the U-boats could not. Many of the U-boats involved never returned to base to file their reports; so historians still struggle to correlate individual reports of the dozens of ships interacting briefly in no fewer than 24 attempted attacks on the night of 5/6 May.
At 2309 "Vidette" made a radar contact at , and a second appeared while closing the first. "Vidette" dropped a pattern of ten depth charges on a submarine seen submerging ahead, and then moved on to drop a pattern of five depth charges on the second contact which became visible at . Historians suggest the first attack destroyed "U-531".
At 0030 "Loosestrife" made a radar contact at . The U-boat turned away when the range reached and fired two torpedoes at "Loosestrife" 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 destruction of "U-192".
At 0252 "Oribi" collided with "U-125" first seen at a range of while investigating an ASDIC contact, but lost contact after the collision. While pursuing an ASDIC contact, "Snowflake" detected "U-125" on radar at 0354, observed heavy conning tower damage by searchlight at a range of , and watched the crew detonate scuttling charges and abandon ship. The escorts chose to continue protective patrolling around the convoy rather than attempting rescue of the U-boat crew assumed to have sunk the "Lorient".
At 0406 "Vidette" made an ASDIC contact at , and made a hedgehog attack causing two explosions. Historians suggest this attack destroyed "U-630".
At 0443 "Sunflower" made an ASDIC contact at and subsequently sighted a surfacing U-boat. "Sunflower" rammed "U-533" and dropped two depth charges as "U-533" attempted to dive. Both "Loosestrife" and "U-533" were able to repair damage and remain at sea.
At 0552 "Pelican" was leading the 1st Support Group to reinforce the convoy escort when it detected a radar contact at . "Pelican" made visual contact at , 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 destroyed "U-438".
"Finke" had already outlasted its usefulness, and faced mounting losses if the attack continued. Realizing his mistake, Dönitz called off the assault on 6 May and ordered "Finke" to retire.
Conclusion.
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 weapons and expertise at their disposal meant that henceforth they would be able not only to protect their charges and repel attack, but also 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 Dönitz 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."