Striking Back: Canada’s Corvettes Take On The U-boats

November 14, 2013 by Marc Milner
The ship’s company of HMCS Assiniboine, Halifax 1941. Lieutenant-Commander  J.H. Stubbs and Rear-Admiral Leonard Murray are in the front row. [PHOTO: LIBRARY AND ARCHIVES CANADA—PA104510]

The ship’s company of HMCS Assiniboine, Halifax 1941. Lieutenant-Commander J.H. Stubbs and Rear-Admiral Leonard Murray are in the front row.
PHOTO: LIBRARY AND ARCHIVES CANADA—PA104510

No one knew it at the time, but the operations of Wolf Pack Hecht in May 1942 marked the recommencement of U-boat attacks on transatlantic convoys (The Wolf Pack Attacks: The Battle For One World War Two Convoy, September/October).

These attacks culminated a year later in the crisis of the Atlantic war—and Allied victory. The first half of this renewed mid-ocean war in the summer and fall of 1942 is not recognized in the dominant Anglo-American literature as a distinct phase. That is probably because the burden of combat during this period fell on Canadians.

This fact was well understood at the time. As the Admiralty’s Monthly Anti-Submarine Report for January 1943 concluded, “The Canadians have had to bear the brunt of the U-boat attack in the North Atlantic for the last six months, that is to say of about half of the German U-boats operating at sea.”

As noted in this series of articles, the U-boats seemed to feed with impunity on inshore shipping in the Canadian zone in 1942. But they also descended on the predominantly Royal Canadian Navy escorted slow convoys in the mid-ocean, and that was no accident. Slow convoys were easy targets and the RCN lacked the ships and equipment to defend them properly as the scale of attacks grew that year.

HMCS Assiniboine, November 1940. [PHOTO: LIBRARY AND ARCHIVES CANADA—PA184010]

HMCS Assiniboine, November 1940.
PHOTO: LIBRARY AND ARCHIVES CANADA—PA184010

However, in the summer of 1942—during a distinctly Canadian phase of the Atlantic war—the RCN more than held its own.

Improvements in the RCN’s mid-ocean capability were in fact evident in the final operations against Wolf Pack Hecht in June. Pursuit of convoy ONS 92, which I described in the September/October issue, drew Hecht westward, towards Newfoundland, and attempts to attack the next two westbound slow convoys, ONS 94 and ONS 96, failed. Both of these were under British escort. Another convoy, ONS 98, managed to slip by unseen. It was not until Wolf Pack Hecht worked its way back east to gain “sea room” that it got its teeth into another convoy, ONS 100.

This 39-ship convoy was escorted by the nominally Canadian group C.1. On this occasion only the senior officer, Lieutenant-Commander J.H. Stubbs, RCN, and his destroyer Assiniboine were Canadian: the old four-stack St. Croix and the corvette Buctouche were delayed by mechanical defects. So Stubbs’s C.1 was comprised of Assiniboine, plus two British and two Free French corvettes. It was, however, no scratch team. This group had operated together on two previous crossings, and Stubbs had worked to mould them into a cohesive unit. It helped that the Allied corvettes had modern type 271 radar.

Three of Hecht’s U-boats made contact with ONS 100 on June 8, and tried to attack it early the next day. None penetrated the convoy. As Clay Blair wrote in his book Hitler’s U-Boat War, “the feisty, battle-wise, radar-equipped corvettes” stopped them. In the process, U-124 torpedoed the French corvette Mimosa, destroying her in a shattering explosion; Stubbs found four survivors the next morning. By then the Admiralty had warned that three U-boats were still in contact. On June 9, Stubbs sent his British corvettes to maximum visibility distance on the flanks of the convoy to drive them off. These sweeps drove off two U-boats, leaving Stubbs with only one to deal with as darkness fell.

With His Majesty’s Ship Dianthus absent in pursuit of its contact, Stubbs placed Assiniboine on the port bow of ONS 100. The British corvette Nasturtium, whose radar had just failed, was on the starboard bow while the Free French corvette Aconit, equipped with the only remaining operational type 271 radar, was astern.

By midnight the convoy was enveloped in fog, which would have been an advantage to an escort with good radar. But the fog blinded C.1, allowing U-94 to slip in and sink two ships before escaping. Dianthus picked up survivors as she rejoined from astern.

The wolf pack lost contact with ONS 100 in dense fog on June 10, until U-124 re-established it the next day, entirely by accident. U-569 sank a straggler astern of the convoy that night, but by then C.1 had been reinforced by Cmdr. Chummy Prentice’s training group, comprised of the corvettes Chambly and Orillia.

Stubbs passed command over to Prentice who patrolled aggressively around ONS 100 and may have driven off U-96 in the process. His efforts did not prevent U-124 from attacking and sinking one final ship in the early hours of June 12. Closeness to land, increased air support and more RCN reinforcements in the form of Bittersweet and Chilliwack brought the battle to a close.

Wolf Pack Hecht launched its final attacks against the next slow westbound convoy, ONS 102. Comprised of 63 ships, it was escorted by the nominally American group A.3, now under Captain Paul Heineman, and was heavily reinforced to handle the large convoy. This time A.3 included three United States Coast Guard cutters and a United States Navy destroyer, supplanted by the Canadian destroyer Restigouche and her high-frequency direction finding set, along with four RCN corvettes: Agassiz, Collingwood, Mayflower and Rosthern. None of the escorts had modern radar, but A.3 was a large and powerful group, and Heineman made good use of Restigouche’s HF/DF.

The six members of Hecht’s group made contact with ONS 102 on June 16. As each made their contact report, Restigouche’s HF/DF operator located them and the escort drove them off. Two U-boats barely escaped with heavy damage after prolonged depth charging. Meanwhile A.3 was joined by Prentice’s training group, fresh from supporting ONS 100 and now augmented by Bittersweet and Chilliwack. ONS 102 was now shepherded by 13 escorts: nine RCN and four American. Heineman tried repeatedly to take command of Prentice’s ships and draw them into his screen, but Prentice refused. He had strict orders from Rear-Admiral Leonard Murray in St. John’s to act as a “striking force” and not be absorbed into any close escort group. And so Prentice conducted sweeps around ONS 102 and ON 103 during the day and provided a distant screen for ONS 102 at night.

Since historians have never done a thorough assessment of the passage of ONS 102 we do not know if Prentice’s efforts were successful. Wolf Pack Hecht abandoned pursuit on June 18, just after U-124 made a submerged daylight attack and sank one ship. We do know that
12 U-boats (Hecht, plus U-boats in transit) had tried to locate and attack ONS 102, and that, with the singular exception of U-124, they failed. Moreover, initial attempts at contact had been disrupted by Restigouche’s HF/DF and two U-boats were seriously damaged.

All in all, it was a good news story for the North American navies.

Corvettes Chambly and Orillia, April 1941. [PHOTO: LIBRARY AND ARCHIVES CANADA—PA105310]

Corvettes Chambly and Orillia, April 1941.
PHOTO: LIBRARY AND ARCHIVES CANADA—PA105310

The successful passages of ONS 100 and ONS 102 drew little—largely muted—criticism from British staff officers. Stubbs had done well with a weak escort in defence of ONS 100, especially on June 9 when the U-boats were known to be in contact. Modern radar helped enormously. Murray urged the naval staff in Ottawa to fit HF/DF to his ships as a top priority. The British understood the need, and had already assigned modern type 271 radar to the RCN at a rate of 10 sets per month. And so it seemed reasonable to expect that these sets would begin to appear on RCN escorts in the mid-ocean.

The staff at Western Approaches Command perhaps also understood that working with the Free French was not easy. Mimosa had made no signal that she was in contact with the U-boat prior to her destruction, and Aconit failed to report a critical radar contact about the same time. In any event, Stubbs—a highly competent regular force officer—had done very well under difficult circumstances. Royal Navy Cmdr. C.D. Howard-Johnston, probably the sharpest critic of the RCN in Western Approaches Command, was reduced to petulant sniping at Murray. The latter’s comment that Nasturtium ought to have pursued a U-boat contact rather than holding its position in the screen was something Howard-Johnston considered a “rather rash generalization.”

There seems to have been nothing to criticize about Heineman’s handling of the escort of ONS 102. In contrast to what happened with ONS 92, Heineman understood and used the HF/DF fixes, and they were instrumental in breaking up the initial pack attack. A dozen U-boats had been held at bay, and they got off one lucky shot in a daring daylight submerged attack. Heineman, who became one of the most capable and successful senior executive officers of the Atlantic war, showed his skill in the passage of ONS 102.

What Howard-Johnston and his colleagues in Liverpool thought of Prentice’s efforts to support ONS 102 and ON 103 remains unclear. The American admiral in Argentia, Vice-Admiral P.M. Brainard, USN, was less than happy about “freelance” RCN operations in his zone. He may well have known that Murray was equally unhappy about Brainard’s operational control in an area where the RCN was the dominant force. Murray’s training group was a very cleverly disguised way for Murray to effect operations without exercising operational command. It was part of a budding campaign to win Canadian control over the northwest Atlantic.

The lessons for the Germans, or at least for Admiral Karl Dönitz, were much clearer: Hecht’s operations were a success. North Atlantic convoys were no better guarded in the summer of 1942 than they had been a year before. The problem of U-boats being located when making their sighting reports (HF) and transmitting their homing signals (on medium frequency) was ‘understood,’ and changes in procedures were introduced to deal with those. For the moment Dönitz was entirely unaware of the type 271 radar or of shipborne HF/DF. The defence of ONS 102 was put down to aggressive patrolling, which suggests that Prentice’s training group may have had an impact after all.

Dönitz was also quick to ascribe German failures to inexperience and rashness. Most of the U-boats operating in Hecht’s group were on their maiden voyages with new captains. Dönitz believed they were prone to bungling approaches to convoys, and generally making U-boat operations around convoys more dangerous than they ought to be.

Battles with Wolf Pack Hecht proved the value of modern equipment, especially type 271 radar and HF/DF, and the importance of powerful escort groups that were able to exploit the tactical information provided by these new sensors. Unfortunately, because the Naval Service Headquarters collection of convoy files was destroyed in the 1960s we will never know with certainty what the RCN staff reaction to this was at the time. Murray was pressing for rapid—if not emergency—modernization of his fleet. But the naval staff minutes and surviving documents suggest the same urgency was not felt 2,400 kilometres away in Ottawa.

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