Convoy ONS5 (North Atlantic, April-May 1943)

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emason
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Convoy ONS5 (North Atlantic, April-May 1943)

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The North Atlantic, April-May 1943

Prologue

From September 1939 until April 1943, Britain had been fighting a loosing battle against the U-boat in the North Atlantic for three and a half years. In 1942 alone, over 1,000 merchant ships, or 5.5 million tons were lost, at the cost of 86 U-boats. Ships were being sunk faster than they could be replaced, and the size of the U-boat fleet was increasing.

In the first three months of 1943, North Atlantic shipping losses were 155 ships at 930,000 tons for 40 U-boats sunk. In March alone, 82 ships at 476,000 tons were lost for 15 U-boats sunk. Britain could not sustain losses on this scale for much longer.

In his memoirs Admiral Doenitz wrote “At the end of March 1943, after three and a half years of war, we had brought the British maritime power to the brink of defeat in the Battle of the Atlantic, and that with only half the number of U-boats we had demanded”.

An Admiralty review later stated “The Germans never came so near to disrupting communications between the New World and the Old as in those first 20 days of March 1943”.

But two months later, in May 1943, for the first time, more U-boats (41) were sunk than ships lost (34). In his memoirs, Admiral Doenitz wrote “On May 24 I ordered them (the U-boats) to proceed, with utmost caution, to the area south east of the Azores. We had lost the Battle of the Atlantic”.

What had happened in such a short space of time to cause this dramatic reversal of fortunes?

Well, nothing really, except for the experience gained in using the weapons and systems currently in operation. The major developments in weapons, aircraft, technology etc. were just staring to come into operation, but not in numbers at this point in time.

But probably the biggest single factor was the advanced training given to escort officers, by the Western Approaches Tactical Unit (WATU), in convoy protection and anti U-boat warfare. This course developed tactics for dealing with all kinds of attack by U-boat and situations developing from them.


The General Situation

Background
Suitable land based aircraft were not available to the Allies in quantity, and those that were had insufficient range to cover convoys the whole way across the North Atlantic. Thus there was an area, south and southeast of Greenland, which became known as the “Mid Atlantic Gap” or “Greenland Gap”, where U-boats could operate free from the danger of air attack. It was in this gap of a few hundred miles that most U-boat patrol lines were positioned ready to intercept both east and westbound convoys.

At the end of April 1943, the number of U-boats available to operate in the North Atlantic reached a high point – 193, of which only about one third would actually be on patrol at any one time. Sixty of which were in the North Atlantic, positioned mainly in the so called “Greenland Gap”. This was the highest number ever to participate in one convoy battle.

British Intelligence
Towards the end of April, Bletchley Park had one of its periodic “blackouts” when the four rotor “Triton” cipher could not be broken, so naval Ultra was not available to the Navy’s Operational Intelligence Centre (O.I.C.). This did not mean that there was no available intelligence about U-boat movements. There were other sources.

For example, every time a U-boat either left of arrived at its base, it was met by an escort which reported the U-boat’s arrival or departure to its base in a cipher that was already broken. Thus the identity and exact number of U-boats at sea was known. It also indicated which U-boats were lost by their non arrival.

A Triton signal from a U-boat, although unintelligible, gave away its position through land based HF/DF intercepts. From this, its route and speed could be estimated, and thus its probable destination.

Because U-boat signals were formalized, the length of a signal gave a clue as to its content. Thus a weather report could be distinguished from a sighting report which was different from a position report. When a convoy was sighted, the necessary sending of many signals alerted O.I.C. to the fact.

The Submarine Tracking Room used all of these sources to estimate the position and numbers U-boats and whether they posed a threat to a convoy. The main purpose of the Submarine Tracking Room at this time was to route convoys away from concentrations of U-boats.

After sighting a convoy, it could take the U-boats a couple of days to concentrate around it, generally giving the O.I.C. enough time to organize reinforcements for the convoy such as air support and escort support groups.

German Intelligence
The German radio and cryptographic service, the Beobachtungsdienst or Bdienst, had been reading the Anglo/American Naval Cipher No.3 since 1941, and had intelligence about most convoys including their sailing dates, routes and destination.

When the Bdienst informed the BdU (Befehlshaber der Unterseeboote, or U-boat Command) about a convoy’s departure date and probable route, the BdU organized available U-boats into patrol lines (sometimes called wolfpacks) across the expected routes to intercept the convoy.

When a U-boat sighted a convoy it sent a sighting report to the BdU, indicating the convoy’s speed and direction, then continued to shadow the convoy, transmitting a radio homing signal. The BdU then signaled other U-boats in the area, directing them to concentrate at a point ahead of the convoy before attacking.

U-Boat Patrol Lines

Because of the multiplicity and transient nature of patrol lines, it is difficult to keep track of the big picture of which U-boats were where at any one time.

Patrol lines were both temporary and mobile; they were constantly being formed, reformed and dispersed as convoys came and went. Each time they reformed they acquired a new name. They were not static, they moved, sweeping the ocean before them to maximize their chances of making an interception.

On May 1, in the Greenland Gap, there were 56 U-boats organized into 4 patrol lines. The following show the patrols active in the area at this time.

Patrol Line “Specht”.
Position: NE of Newfoundland, to intercept SC.127 and HX.235.
Active from April 19 to May 4.
Consisted of 24 U-boats.
On May 5 most go to “Fink” and some to “Amsel” 3 and 4.

Patrol Line “Amsel”.
Position: East of Newfoundland, southeast of Specht, to intercept HX.235 and SC.128
Active from April 22 to May 3.
Consisted of 16 U-boats.
On May 4 this split into four lines, “Amsel” 1,2,3 and 4.

Patrol Line “Star”.
Position: SE of Iceland, to intercept northern routed convoys.
Active from April 24 to May 1.
Consisted of 16 U-boats.
On May 3 all go to “Fink”.
.
SpechtStar.jpg
.
Patrol Line “Fink”.
Position: South of Greenland, to intercept SC.128.
Active from May 3 to May 6.
Consisted of 28 U-boats from “Specht” and “Star”.

Patrol Lines “Amsel 1-4”.
Position: South and southwest of Fink.
Active from May 3 to May 6.
Consisted of 4 groups of 5 or 6 U-boats.
Formed from lines “Amsel” and “Specht”
.
FinkAmsel.jpg
.
Convoys at Sea
During this critical period, there were about ten convoys en route, arriving or departing, providing no shortage of potential targets for the U-boats.

Eastbound convoys from Halifax, Nova Scotia to U.K.
HX.234, HX.235, HX.236, HX.237.

Eastbound from Halifax to U.K. (Slow)
SC.127, SC.128, SC.129.

Westbound from U.K. to North America
ONS.5, ON.180, ON.181.

But, if there is one of these convoys, in its battle with the U-boats, which can be described as a turning point in the Battle of the Atlantic, it has to be convoy ONS5. Captain Stephen Roskill, the naval historian, described it thus:-

The 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.”

(To be continued . . .)
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Bill
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Re: Convoy ONS5 (North Atlantic, April-May 1943)

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CONVOY ONS5 (April 22 to May 12, 1943)

Convoy ONS5 (Outward to North America Slow), code name “Marfleet”, was the object of the biggest convoy battle of the war.

The convoy was made up of 45 ships including two escort refueling tankers, the majority being in ballast. There were ships from Britain, America, Norway, Holland, Denmark, Poland, Greece, Jugoslavia and Panama. They sailed from the ports of Milford Haven, Liverpool, the Clyde, Oban and Londonderry.

The convoy Commodore was Captain J. Brooks RNR, sailing in the Norwegian ship RENA.

The Route
The two previous ON convoys had used a northerly route to avoid concentrations of U-boats. The route chosen for ONS5 was even further north to avoid U-boats remaining from the previous convoy routes, and to take the greatest advantage of air cover from aircraft based in Iceland.

After assembling in the North Channel, they would head NW into the Atlantic for 300 miles, then West to Cape Farewell, Greenland (1,000 miles), then SSW to the Grand Banks of Newfoundland (1,000 miles), then SW to their destination Halifax, Nova Scotia (500 miles). Total distance was about 2,800 miles.

The Escort for ONS5
There were three types of escort groups:-

The Close Escort Group.
This is the close escort, sometimes called “the mid-ocean escort”, which sails with the convoy for most of its time at sea, whose prime purpose is the convoy’s “safe and timely arrival at its destination”.

Escort Group B7 under Commander Peter Gretton, comprising Destroyers: HMS Duncan, HMS Vidette. Corvettes: HMS Sunflower, HMS Snowflake, HMS Pink, HMS Loosestrife. Frigates: HMS Tay. Trawlers: HMT Northern Gem, HMT Northern Spray.

(Note: Commander Peter Gretton was previously in command of the destroyer HMS Wolverine, when she rammed and sank the Italian submarine Dagabur in the Mediterranean during Operation Pedestal.)

Escort Support Groups.
These were hunter killer groups of four to eight warships whose purpose was to hunt to destruction any U-boat detected near a convoy, while the escorts continued with protecting the convoy. Usually, they did not sail with the convoy, but were directed by the O.I.C. to one deemed to be in danger. While operating with the convoy they were under the command of the close escort.

Two Support Groups were used at different times for this convoy:-
Support Group EG1, (Commander G.N. Brewer), comprised of Frigates: HMS Wear, HMS Jed, HMS Spey. Sloops: HMS Pelican. Cutters: HMS Sennen.

Support Group EG3 (Captain J.A. McCoy), comprised of - Destroyers: HMS Impulsive, HMS Offa, HMS Oribi, HMS Panther and HMS Penn.

Local Escort Force

These groups usually took over from the Mid Ocean Escort Group, giving them a much needed relief, and escorted the convoy the rest of the way to its destination. When the convoy was westbound, they met at the Western Ocean Meeting Point (WESTOMP), about 350 miles due east of Newfoundland.

Canadian Western Local Escort Force (WLEF), comprised of – Corvettes: HMCS Barrie, HMCS Galt, HMCS Buctouche and HMCS Cowichan.


THE VOYAGE

April 21
The 42 vessels of the convoy sailed from their ports to rendezvous with their escort at the convoy assembly point at the entrance to the North Channel.

April 22
They assembled off the island of Islay into a formation 12 columns wide and 3 and 4 ships deep, then headed north west into the Atlantic at 7 knots. One ship returned to the Clyde with engine problems.

April 24

A Hebrides based Coastal Command Flying Fortress of 206 squadron, sweeping ahead of the convoy, spotted and sank U710 a short distance ahead. U710 was in transit to its patrol area in the North Atlantic and was probably unaware of the convoy’s presence. A case of being in the wrong place at the wrong time. Later that day the weather started to deteriorate.

April 25
A strong gale was blowing and the convoy, struggling to keep formation, slowed to 2-3 knots. Several ships were damaged in the heavy seas, and two collided, one of which was detached to Iceland.

April 26
The bad weather continued and dispersed ships were rounded up back into formation. HMS Vidette joined the convoy from Iceland with three more merchantmen. Hudson aircraft from Iceland were now providing air cover.

At noon, BdU changed their “Triton” settings, causing an intelligence “blackout” for Bletchley Park.

April 27
The weather moderated slightly, allowing some of the escorts to refuel. A straggler was sent to Iceland.

April 28
At 09.00, when southeast of Iceland, ONS.5 was sighted by U650, the northernmost U-boat of the “Star” line. Several HF/DF contacts were made by the escort, one from close ahead. Commander Gretton ordered HMS Snowflake to hunt down this bearing, and the convoy to alter course by 35 degrees to starboard.

From noon onwards, many more HF/DF contacts were made and hunted down, but nothing was found. So at 16.00 the convoy resumed its original course.

Several more HF/DF contacts were made and hunted down fruitlessly, except on one occasion when HMS Duncan saw a U-boat’s conning tower and dropped 10 depth charges on its estimated position.

In the evening, multiple HF/DF contacts were made from all positions around, and Commander Gretton ordered the night cruising stations. Many more radar contacts were made and investigated, dropping depth charges “just to give them something to think about”.

Back at O.I.C. the Submarine Tracking Room saw a dangerous situation developing and ordered the 3rd Support Group EG3 from St. Johns, Newfoundland to assist.

(Note: The main escort tactics at this time appear to be to attack aggressively with a single ship every contact made, to make the U-boat submerge, break off their attack and hopefully loose contact with the convoy. If they destroyed or damaged the U-boat, so much the better, but it was not a priority; protecting the convoy was. The escort would then return to the convoy so as not to leave their position unprotected for too long.)

April 29
Between 00.00 and 03.30, there were six attempted U-boat attacks, all were detected by radar, and all chased down and depth charged. During one of these counter attacks, both U386 and U528 were damaged and had to return to port. (U386 made it by May 11, but U528 was sunk while crossing the Bay of Biscay.)

At 05.50 HMS Snowflake chased down another ASDIC contact, dropping two ten-charge patterns, severely damaging U532, requiring her to return to port.

At 07.30 the SS McKeesport was torpedoed by U258 and later sunk by gunfire and depth charges by HMS Tay. All the crew were picked up by the trawler HMT Northern Gem.

HF/DF contacts showed three or four U-boats trying get ahead of the convoy, and a couple more on the port side.

April 30
At 01.00, HMS Oribi arrived, detached from convoy SC.127 as extra support.

At noon the weather turned worse, and by 21.00 a full westerly gale was blowing, preventing the escorts from refueling.

May 1
At 01.00 HMS Snowflake obtained a close radar contact, chased it down and engaged a surfaced U-boat with gunfire before it submerged and escaped.

By afternoon, a full force 10 storm was now blowing with 30ft waves scattering the ships of the convoy, which was able to make 5 knots only, and the escorts were unable to refuel.

The bad weather was also affecting the U-boats as no U-boat contacts were made. The “Star” patrol line was dispersed, its U-boats joining the “Fink” line on May3.

May 2
The weather was now moderating and the convoy was able to make 5 knots. In the previous 24 hours they had progressed by only 20 miles. Several times they “hove to”. The escorts were sent to round up the stragglers located by a Liberator from Iceland. But again it was still too rough to refuel the escorts, with the additional hazard of having to make abrupt changes in course to avoid ice floes and bergs.

At 20.00 the 3rd Support Group EG3 had joined the convoy from St. Johns, Newfoundland.

May 3
Gale force winds from the southwest were still battering the convoy, and it was scattered again. Only 32 ships remained in formation.

At 15.00, because it was still too rough to refuel, or transfer ship, Commander Gretton in HMS Duncan handed over command to Lieutenant Commander Sherwood in HMS Tay, and departed for St. Johns in Newfoundland to refuel. Later three more escorts had to leave to refuel, HMS Impulsive to Iceland, HMS Panther and HMS Penn to Newfoundland. Also, HMT Northern Gem was detached to Newfoundland with her survivors from SS McKeesport.

(Note: HMS Duncan was one of the two HF/DF equipped escorts, the other being HMS Tay. Fortunately, the recently arrived HMS Oribi was similarly equipped so HF/DF contacts could still be located.)

The First Support Group (EG1) was ordered out from St. Johns to reinforce ONS5.

The convoy traversed the “Greenland Gap” without being attacked. Fortunately, the weather had simply been too bad for the U-boats in which to operate, but was now improving and the convoy increased speed to 6 knots. Apart from the bad weather, the lack of U-boat activity was partially due to the increasing number of air patrols from Newfoundland which attacked several U-boats, forcing them to submerge.

The “Star” and “Specht” lines were now ordered to merge into the new “Fink” line, and be in place by 08.00 on May 5 with its 28 U-boats stretching across 380 miles. Unknown to BdU, this was right across ONS.5’s route, but was initially intended to intercept convoy SC.128 which, thanks to O.I.C. changed course to the north, and evaded them all.

The “Amsel” patrol line was split into four separate lines south of “Fink”, reinforced by some U-boats from the “Specht” line.

Doenitz signaled “Do not hold back, something can and must be achieved with 31 boats.”

(To be continued . . .)
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Bill
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Re: Convoy ONS5 (North Atlantic, April-May 1943)

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The Voyage (continued)

May 4
The weather had cleared and the convoy had been reformed, with its 30 ships into ten columns. Fifty miles astern, a separate group of four stragglers, escorted by HMS Pink proceeded independently from the main formation with its own route.

At 16.00, ONS.5 steamed right into the centre of the “Fink” line (which was not yet fully in position) and was spotted by U628. Thinking this was convoy ON.180, BdU ordered the “Fink” U-boats to attack, together with both the “Amsel 1” and “Amsel 2” U-boats. The initial conditions for a U-boat attack have never been more favourable. Doenitz signaled “You are better placed than you ever were before”.

Meanwhile, Lieutenant Commander Sherwood in HMS Tay was aware of many HF/DF contacts made on the port and starboard bows, beam and quarters. Communications failed between HMS Tay and the other HF/DF escort, HMS Oribi, so accurate “fixes” could not be made.

Air cover from Newfoundland now made itself felt when, at 18.00, an RCAF Canso (a Canadian built Catalina) detected U209 by radar from seven miles away. U209 was ten miles behind a straggler from ONS.5 when spotted. The Canso attacked the U-boat severely damaging it, eventually sinking alone on May 7. Another Canso attacked U438 slightly damaging it.

There was no attack during daylight by the 15 U-boats already in contact with the convoy, who waited instead for darkness, by which time many more had arrived.

When night came, MV Lorient, a straggler, was sunk by U125 with no survivors. The sinking was unobserved so went unnoticed.

At 22.00 Doenitz signaled “I am certain that you will fight with everything you’ve got. Don’t overestimate your opponent, but strike him dead”.

May 5
At 00.20, HMS Vidette detected U514 on her radar at 3,600 yards, attacked with depth charges and damaged her.

At 00.30, MV North Britain, a straggler with boiler trouble, was torpedoed by U707. 11 survivors were picked up by HMS Northern Spray.

At 00.45, MV Harbury, was torpedoed by U628 and sunk later, at 12.30, by gunfire from U628. 44 survivors were picked up by HMT Northern Spray.

At 00.50 HMS Vidette got another radar contact, this time it was U662 that was attacked, but submerged only just in time to avoid being rammed. The subsequent depth charge attack missed U662 but HMS Vidette had the good fortune, unbeknown to her, of causing enough damage to the nearby U732 to force her to return to base.

At 01.00, SS West Maximus was sunk by U264. 56 survivors were picked up by HMT Northern Spray.

At 01.00, MV Harperley was sunk by U264. 38 survivors were picked up by HMT Northern Spray.

(HMT Northern Spray was later ordered to Newfoundland with all its 143 survivors on board.)

At 02.20 MV Bristol City was by sunk by U358. 29 survivors were picked up by HMS Loosestrife.

At 02.50 MV Wentworth was torpedoed by U358 and later sunk by U264. 42 survivors were picked up by HMS Loosestrife.

At 05.00, HMS Snowflake detected and pursued U270 on the surface, forced it to dive, then attacked the ASDIC contact with depth charges of which she was running short. HMS Oribi then took over the attack, during which U270 was damaged enough to send it back to port.

At 07.00, the escort ships of B7 resumed their day sailing stations. Many HF/DF contacts showed the convoy was still surrounded.

At 10.10, HMS Oribi obtained a radar contact at 5,000 yards, upon investigating found three surfaced U-boats which dived, and were depth charged. Despite no result, HMS Oribi persisted and regained contact at 12.45 and attacked twice more, again with no result. (She had in fact attacked four U-boats, U223, U231, U621 and U634).

At 11.55, HMS Pink, trailing some 80 miles astern of the main convoy with her own mini convoy of four ships, obtained an ASDIC contact at 2,200 yards. Over the next two and a half hours she dropped salvoes of depth charges, tried the Hedgehog which misfired, tried the hedgehog again which fired but all the mortars exploded on contact with the surface of the sea.
(Note: For many years after, she was credited with sinking U192, but it is now thought to have been U358 that she damaged so severely that it was ordered to return to port.)

At 12.40, MV Dolius was sunk by U638. Two minutes after the attack, HMS Sunflower picked up an ASDIC contact in the middle of the convoy at 1,200 yards and chased it down, dropping a ten-charge pattern with no apparent result, returning to her escort position after picking up 44 survivors from the sinking. Later reassessment showed that HMS Sunflower had in fact sunk U638 in this attack, unbeknown to her.

(Tactical note: When a ship in the middle of the convoy is torpedoed (as MV Dolius was), the escorts perform a manoeuver called an “Artichoke”. This entails the leading escorts only, making an immediate, simultaneous 180 degree turn, passing both outside and through the convoy. HMS Sunflower passed though the convoy and located U638.)

By this time, Bletchley Park had found a way back into “Triton”, and the intelligence started to flow once more, but the signals were decoded too late to be of any use to ONS5. The flurry of U-boat signals HF/DF’ed had already told O.I.C. what was happening and informed Sherwood of a very large concentration of U-boats in his area, as if he didn’t already know.

There were in fact 40 U-boats, the largest number ever to be assembled against a single convoy. There were more U-boats gathered around the convoy than the 26 ships remaining in it, and threatened to overwhelm the escorts.

In the afternoon, Doenitz signaled “Hurry - there are 40 of you - otherwise you will loose this convoy. The battle can’t last long since the sea space left is short, so use every opportunity to the fullest with all your might.” In effect ordering them to attack in daylight.

At 14.50, SS West Madaket, one of HMS Pink’s mini convoy, was torpedoed by U584. 61 survivors were picked up by HMS Pink, who afterwards sank the merchantman with depth charges.

At 19.50, MV Selvistan was sunk by U266. 40 survivors were picked up by HMS Tay.

At 19.50, MV Gharinda was sunk by U266. 92 survivors were picked up by HMS Tay.

At 19.50, MV Bonde was sunk by U266. 12 survivors were picked up by HMS Tay.

With the sudden loss of three ships, Commodore Brook immediately ordered a 90 degree turn to port, resuming normal course after one hour.

At 20.40, HMS Offa acquired an ASDIC contact and in the next 2 hours made five large pattern attacks, damaging U266.

Two hours after dusk, the remaining 23 ships of the convoy reach a fog bank, which effectively screened it from the U-boats, but the escorts could still “see” the U-boats with their Type 271M centimetric radar which the U-boat’s radar warning receiver “Metox” was unable to detect, and so the hunters became the hunted.

At 23.20, HMS Vidette got a radar contact at 7,200 yards, attacked with a ten-charge pattern and sank U531.

In the next four hours HMS Vidette made radar contact four times. Each time she spotted a surfaced U-boat and attacked with gunfire and depth charges.

May 6
At 00.30, HMS Loosetrife obtained a radar contact at 5,200 yards, pursuing the U-boat until, at 500 yards, U192 was spotted and HMS Vidette prepared to ram. Failing to make contact, HMS Vidette fired a shallow ten-charge pattern and U192 surfaced, when there was an internal explosion and she sank.

At 02.50, a close ASDIC contact was obtained by HMS Oribi. Turning towards it, she saw a U-boat about 200 yards away and prepared to ram. HMS Oribi struck U125 abaft the conning tower, damaging her own bows and doing unknown damage to the U-boat which then disappeared. Shortly afterwards, HMS Oribi obtained an ASDIC contact at 1,100 yards and dropped a single deep set charge. At 03.30 the search was abandoned.

AT 03.30, HMS Snowflake obtained three radar contacts in quick succession. But with only two depth charges remaining, she engaged the first with gunfire and dropped a single charge. The second she also engaged with gunfire but lost ASDIC contact, by which time the third contact had disappeared. HMS Sunflower was ordered to assist her.

At 03.35, while making an ASDIC sweep, HMS Snowflake made another radar contact. Visibility was very bad, but when the range had closed to 100 yards, she switched on her searchlight and saw a heavily damaged U-boat low in the water. It was U125 which HMS Oribi had previously rammed. Being too close to use her guns, HMS Snowflake withdrew, and as she did the U-boat started to sink with some crewmen abandoning her and others running towards the forward gun deck, until a burst of Oerlikon fire dissuaded them, then everyone jumped overboard. Five scuttling charges were heard and the U-boat sank. HMS Snowflake informed HMS Tay about the survivors, who replied “Not approved to pick up survivors”. So when U125 finally sank, it was with all hands.

At 04.10, HMS Vidette acquired an ASDIC contact at 800 yards and attacked with her Hedgehog. Two underwater explosions were heard and U630 was sunk.

At 04.45, HMS Offa acquired an ASDIC contact at 1,200 yards range. Sighting the U-boat at 300 yards with its searchlight, HMS Offa prepared to ram, and struck the U-boat between the tower and stern. Unfortunately HMS Offa suffered more damage to herself than she inflicted on U533 who survived with only minor damage to fight another day.

At daybreak, Support Group EG1 arrived from St. Johns, Newfoundland, and was immediately involved in the action when, at 05.50, HMS Pelican obtained a radar contact at 5,300 yards. Fifteen minutes later, a U-boat was sighted on a reciprocal course at 300 yards. When only 100 yards away, the U-boat crash dived as HMS Offa engaged her with gunfire. Turning into the dive swirl, HMS Offa fired a shallow set, ten-charge pattern. Coming round for a second attack, she fired a nine-charge, deeper set pattern, and was rewarded a few minutes later when three small underwater explosions were heard, followed nine minutes later another one which shook the ship. The victim was later confirmed as sunk, and identified as U438, which had been previously damaged by a Canadian Canso aircraft on May 5.

From the evening of the May 5 to the morning of May 6, there were 25 attempted U-boat attacks; all were repulsed, with escorts making 15 attacks and sinking six U-boats, most of which were surprised on the surface by a warship bearing down on them out of the fog at distances as little as 300 yards.

On the morning of the 6th, with the coming of daylight, the U-boats abandoned their pursuit.

At 15.00, ONS5 and its escorts arrived at the Western Ocean Meeting Point (WESTOMP) where they were met by the Canadian Western Local Escort Force (WLEF) who relieved the close escort group B7, taking over escort duties for the remainder of the voyage. The convoy was not threatened again and proceeded unmolested the rest of the way to Halifax.

May 9
The close escort group B7 parted company with the convoy and headed towards St. Johns, Newfoundland.

May 12
ONS5 with its local escort arrived at Halifax.

(To be continued . . .)
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Bill
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Re: Convoy ONS5 (North Atlantic, April-May 1943)

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Losses

Ships lost to U-boats (13)
SS McKeesport (U258), MV Lorient (U125), MV Harperley (U264), SS West Maximus (U264), MV Bonde (U266), MV Gharinda (U266), MV Selvistan (U266), MV Bristol City (U358), MV Wentworth (U358/U264), SS West Madaket (U584), MV Harbury (U268), MV Dolius (U638), and MV North Britain (U707).

U-boats lost to escorts (6)
U531 - depth charged by HMS Vidette.
U192 - depth charged by HMS Loosestrife.
U125 - rammed by HMS Oribi, and sunk by gunfire from HMS Snowflake.
U630 - Hedgehogged by HMS Vidette.
U638 - depth charged by HMS Sunflower.
U438 - depth charged by HMS Pelican.

U-boats lost to aircraft (2)
U710 (Fortress from 206 Squadron) and
U209 (RCAF Catalina).

(There were no survivors from any U-boat sunk)

U-boats severely damaged and returned to port (7)
U358, U386, U532, U528, U270, U732 and U258.
(The damaged U528 was returning to its home port when, on May 11, it passed too close to convoy OS47 (Liverpool to Freetown) and was attacked by a Halifax of 58 Squadron with depth charges causing further damage and was finally sunk by HMS Fleetwood, who picked up 45 survivors.)

U-boats lightly to heavily damaged (11)
U413, U514, U648, U438, U226, U223, U533, U634, U266, U267 and U575.


Summary
The battle for ONS5 was a turning point in the Battle of the Atlantic. Although thirteen ships were lost, with forty U-boats attacking there would have been many more were it not for the training, skill and determination of the escorts.

Significantly, a very large “wolfpack” has been defeated by the surface escorts only. The Germans blame their defeat on the fog and radar, but this should have been anticipated as fog is the normal weather conditions for this part of the Atlantic, and it was the Germans who chose the place and time of the battle.

From a total of 40 U-boats assembled to attack, only 15 were ever in a position to make an attack; the others being thwarted by the aggressive tactics of the escort. It is interesting to note that just one U-boat (U438) was sunk by the Support Groups, while the Close Escort B7 sank four, with one shared.

The main weapons used were HF/DF, ASDIC and radar for detection, with the depth charge and Hedgehog for destruction. These were not new weapons, although the depth charges were more powerful types, but with the advanced training provided by the Western Approaches Tactical Unit (WATU), escorts became better at using them effectively.

(Note: The new depth charges were filled with Torpex instead of Amatol, which increased the effective kill range from 20ft to 26ft, and the damage range from 40ft to 52ft. Also new detonating pistols increased their depth from 550ft to 700ft.)

A remarkable prediction was made on 2 February 1943 by Rodger Winn, Director of the Submarine Tracking Room in a paper entitled “Appreciation for the period May to August 1943”.

Paraphrasing him, he said that “For this period, U-boats would concentrate between Newfoundland and Iceland; and there would be no change in BdU’s policy unless U-boats losses exceeded 15%, whereupon the change would be sudden and almost complete”.

In May 1943 U-boats losses were 30% of all those operating in the North Atlantic, when Admiral Doenitz admitted defeat and ordered all U-boats from the North Atlantic.

The following shows just what a turning point April/May 1943 was.

Wartime U-Boat Losses (All causes)
1939 - 9 U-boats lost.
1940 – 24 U-boats lost.
1941 – 35 U-boats lost.
1942 – 86 U boats lost.
1943 – 243 U-boats lost.
1944 – 250 U-boats lost
1945 - 120 U-boats lost.

Or looking at it another way; up to April 1943 (three and a half years of war) 194 U-boats were lost; after then (2 years to end of war) the figure is 573 lost.

Postscript
After their battle with ONS5, the North Atlantic U-boat patrol lines were reformed, with U-boats of the “Fink” line reformed as the “Inn” and “Donau” lines. On May 19, the U-boats of the “Donau 2” line attacked the eastbound convoy SC.130 (escorted by Peter Gretton’s B7) southeast of Cape Farewell, Greenland without success, but lost three U-boats in the process.

One of them, the U954 on its first war patrol, was sunk by HMS Sennen and HMS Jed with depth charges. The entire crew was lost, amongst whom was 22 year old Leutnant zur See Peter Doenitz, the youngest son of Admiral Doenitz. Five days later, Admiral Doenitz admitted defeat and withdrew the U-boats.
Best wishes
Bill
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jbryce1437
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Re: Convoy ONS5 (North Atlantic, April-May 1943)

Unread post by jbryce1437 »

A nice piece of research and thanks for posting it here Bill.

Jim
HMS Raleigh 1963 , HMS Collingwood 1963 & 67 , HMS Ark Royal 1964-7, HMS Undaunted 1968-71, HMS Victory (Fleet Maintenance Group) 1971-72, HMS Exmouth 1972-74
JEM, EM, OEM, LOEM, POOEL
Then 28 years in the Fire Brigade
Retired since 2002
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emason
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Re: Convoy ONS5 (North Atlantic, April-May 1943)

Unread post by emason »

jbryce1437 wrote: Sat May 29, 2021 5:03 pm A nice piece of research and thanks for posting it here Bill.

Jim
Thanks Jim. Much appreciated. :D
Best wishes
Bill
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