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The Wolf Packs: Navy, Part 26

An undated photo showing a U-boat in the North Atlantic during World War II. [PHOTO: BIBLIOTHEK FUR ZEITGESCHICHTE, STUTTGART]

An undated photo showing a U-boat in the North Atlantic during World War II.

Contrary to what some historians suggest, the Royal Canadian Navy’s ambitious plans in late 1940 for a navy built around fleet-class destroyers and cruisers were not out of sync with developments in the war. In fact, even as the Canadian naval staff planned to acquire cruisers and modern fleet-class destroyers, the German pocket battleship Scheer attacked Allied convoys just east of the Grand Banks.

In November, in one of the dramatic moments of the war at sea, Scheer sank the armed merchant cruiser Jervis Bay while attacking convoy HX 84. By December, the heavy cruiser Admiral Hipper was trolling the convoy lanes north of the Azores, and in late January 1941 the battle cruisers Scharnhorst and Gneisenau sortied for two months of raiding in the central North Atlantic. These operations by large warships, co-ordinated with U-boats and German maritime airpower in a combined arms assault on Allied shipping, lasted until the destruction of the Bismarck at the end of May 1941.

It was this phase of the war, coming hard on the heels of the Battle of Britain, that Winston Churchill dubbed The Battle of the Atlantic. He saw it as a discrete and well-defined struggle over Britain’s basic survival, and he was right, although the moniker has since been applied to the whole Atlantic war. The period from August 1940 through the early summer of 1941 was, nonetheless, the one time when the Germans had a clear and attainable strategic goal at sea: knock Britain out by cutting off her lifeline. Nothing in the RCN’s ambitious fleet plan reached maturity in this phase of the war. Certainly the RCN could do little to stop the leviathans of the Kriegsmarine roaming the broad Atlantic, threatening to devour in one bite anything too small to fight or too slow to run. That was the job of the British battle fleet.

U-100 was rammed by a British destroyer in 1941. [PHOTO: BIBLIOTHEK FUR ZEITGESCHICHTE, STUTTGART]

U-100 was rammed by a British destroyer in 1941.

Instead, the real problem for the Allies’ small ships was the German submarine: a problem that would endure for the course of the war. With operating bases in Norway and France, the capability of Germany’s U-boats doubled virtually overnight. Crucial Allied shipping lanes could be reached in a matter of days, time on station increased, and there was no need to run the gauntlet of the British blockade while returning to base.

The British reaction to the German presence along the European littoral was to close its southern and eastern ports to most traffic, and re-route all oceanic shipping into western ports. This was more complex and difficult than it sounds. In 1939, London was Britain’s major port, while traffic from the Mediterranean and south Atlantic relied on use of the English, Bristol and George’s channels to gain easy access to their destinations. What made the whole southern and eastern port system of Britain untenable in 1940 was not the immediate presence of the Kriegsmarine along the French coast, but Luftwaffe squadrons operating from French air bases. Their most dramatic success in the fall of 1940 came on Oct. 26 when the 42,000-ton Canadian Pacific liner Empress of Britain was bombed and severely damaged 70 miles west of Donegal, Ireland, by a four-engine very long-range FW 200 Condor. The crippled liner was sunk two days later while limping towards a British port, by torpedoes from U-32: she was the largest Allied troopship lost during the war.

Closing the southwestern approaches was simply a matter of re-routing shipping, but re-orienting Britain’s internal transportation system was a far more complex problem. Railway personnel and rolling stock, longshoremen and cargo handling equipment from London, Southampton, Portsmouth, Chatham, Hull, Newcastle and Edinburgh and elsewhere had to be moved to Glasgow, Liverpool, Belfast, Bristol and other western ports. This took time and it had to be done while Britain endured the Blitz—itself part of the whole campaign to beat Britain into submission. In the event, the sharp decline of imports experienced by Britain during this phase of the war owed more to these factors than to the depredations of the Kriegsmarine at sea.

However, the reliance on a single focal point of entry north of Ireland—the so-called western approaches—for all oceanic shipping bound to or leaving from Britain made her overseas trade uniquely vulnerable, and the Germans took full advantage of that vulnerability by launching a complex and highly successful air, surface and sub-surface assault.

Britain’s second reaction to the intensification of the attack on its imports was, therefore, to expanded and extend the convoy system. On Aug. 15, the first of a new series of inbound convoys for slow shipping from Canada was started. This SC series, so named because they assembled at Sydney, N.S., in Cape Breton, collected ships slower than the nine knots required of the HX series, but able to sustain at least seven knots. Anything slower was still on its own. The RCN provided anti-submarine escort for the SC series to the Grand Banks, where, as with the HX series, an oceanic escort to guard against large raiders joined for passage of the mid-Atlantic. On the eastern side—the dispersal point for outbound oceanic convoys under anti-submarine escort—moved progressively westward, from 12 degrees, to 15 and then 20, while coastal convoys were organized around the British Isles.

While the British moved to get more shipping under escort protection, the Germans picked a steady harvest from both escorted and unescorted shipping in the western approaches through the late summer of 1940. U-boat aces like Otto Kretschmer, Günther Prien, Joachim Schepke and Fritz Lemp, operating independently, averaged about 25 ships each per month. But the Allied trade protection system was ripe for exploitation, and by late September the Germans demonstrated its vulnerability in a series of landmark battles.

The architect of the German U-boat campaign in World War II was Karl Dönitz, a gifted submariner and inspiring leader. Born in 1891, Dönitz joined the German navy in 1910, and by 1918 was in command of a U-boat in the Mediterranean. It was there, faced with the problem of Allied trade convoys, that young Dönitz hatched the idea of using his U-boat to attack at high speed on the surface. Moreover, he theorized that a group of submarines handled this way would enjoy considerable success against convoys at night. He attempted to put this idea into practice south of Sicily in October 1918, in a two-sub attack on a British convoy. When his colleague failed to show up, Dönitz went ahead with the attack. His U-boat, UB-36, was sunk and Dönitz was captured, but the experience did not shake his faith in the idea of group attacks on the surface on convoys at night. He got the chance to prove his idea when he became head of Nazi Germany’s new submarine service in 1935.

In the years before WW II, Dönitz tinkered with his idea for pack attacks, and even wrote a book on it, which the Allies seemed to have missed. But the real test came under wartime conditions. In October 1939, he ordered six U-boats to assemble off Ireland and conduct pack operations under tactical command of Werner Hartmann in U-37. Unfortunately for Dönitz, the pack failed to assemble: three U-boats were sunk en route to the rendezvous, and one failed to show, leaving only U-37 and another sub to make the first faulty attempt at a Wolf Pack against HG 3.

The second attempt in November fared even worse and Dönitz temporarily gave up the idea. For the moment, at least, there were just too many targets, too few torpedoes, and the idea of local control of the pack at sea was unworkable.

Bases in France and Norway and the concentration of British shipping into one embattled route north of Ireland gave Dönitz a chance to renew his pack concept in the late summer of 1940, and it proved a resounding success. The idea was simple enough. There were three key problems associated with trying to attack a convoy with U-boats in the broad reaches of the ocean: initial location, assembly of the pack around the convoy and the actual attack itself. Although wartime photos of convoys show ships practically filling the sea—at least filling the camera lens—the convoys were actually quite small in the vastness of the ocean. Finding them was a major challenge, especially from the low conning tower of a sub. It was for this reason that individual U-boats usually operated inshore and submerged, allowing the targets to come to them.

Dönitz’s solution to finding targets in the open ocean was to deploy his U-boats in a line perpendicular to the shipping route, and controlling their movement from a headquarters ashore. In order to make this work, regular radio traffic between the subs and their HQ was crucial. U-boat commanders had to transmit noon positions daily, and weather reports when asked. In return, Dönitz’s HQ passed along orders, shifting the position of the line based on the latest intelligence. If all went right, the U-boat patrol line would be placed squarely in front of an approaching convoy, and one of the subs would report its position course and speed. Initial contact was usually visual, but it was possible for U-boats to use their sonar system to get a general fix on the convoy’s machinery noise, and as the war progressed they could do much the same with the escort’s radar signals. In the evolving game of ‘cat and mouse’ between convoy routers and German operational plotters, initial contact was often the most difficult task and many a convoy slipped around or through a patrol line undetected.

Once contact was made, the U-boat that made the sighting was usually tasked as a shadower. This meant sending regular position reports to HQ and transmitting a medium frequency direct finding signal so the rest of the pack could home in. The process of collapsing the pack on the convoy was directed from its shore-based HQ which tracked and recorded each contact report as the submarines found their target. All of the extensive radio traffic associated with these first two phases of a pack operation was vulnerable to intercept by the Allies and to plotting by direction finding stations on shore. However, Dönitz was fully confident the system was foolproof under operational conditions. Radio signals were sent using the highly sophisticated ciphering machine known as Enigma.

Enigma employed a series of alpha-numeric rotors connected in turn to cables that had to be inserted into a socket board in the prescribed manner for the day. The alignment of the rotors and the connections of the cables into the socket board changed daily according to a code book, so that when the operator struck a number or letter on the keyboard a totally different letter or number would light up on the display panel. The combination of three rotors and the cable connection produced tens of millions of possible permutations. Dönitz understood it was possible to decipher signals sent by Engima machines, but assumed this would never be done quickly enough or in sufficient volume to affect operations.

The intelligence the Allies gleaned from listening to signals sent from U-boats at sea was a greater a concern for the Germans. It was possible to accumulate important data from studying the pattern of operations and through land-based DF stations to obtain a rough estimate of the number and general location of U-boats. This kind of plotting and traffic analysis would produce useful intelligence, but it was also unavoidable. Moreover, in 1939 shore-based stations could only estimate positions to within about 50 miles, and no one had yet developed a DF set small enough for a ship. So Allied ‘DF’ing’ could never produce tactical intelligence. In any event, the presence of U-boats would be revealed by their attacks. So the reliance on radio communications was a trade-off, and in 1940 the benefits were almost entirely on the German side.

The final act of the pack operation was the attack, when U-boats were cut loose from their wireless ‘leash’ and the ‘sea wolves’ earned their nickname. Ideally, Dönitz assembled as many U-boats as possible around the convoy before turning them loose. There was no attempt after 1939 to co-ordinate the pack attack at the tactical level, it was just too impractical. Rather it developed in accordance with local conditions and the approach route of the U-boats in contact. The attack then came at night and preferably from the dark side—allowing them to approach against a totally black sky while the convoy lay silhouetted against moonlight.

In practice, attacks often came in waves throughout the night as U-boats, often trimmed down so that only their conning tower remained above the water, raced through the escort screen and into the columns of ships. The objective during that high-speed run was to fire all four bow torpedoes and, if possible, the two stern tubes as well. Once the ‘fish’ were all gone, the U-boat made good its escape by either running astern of the convoy or—if it was pursued by an escort—diving amid the tangle of wakes left by the merchant ships.

This system was not entirely perfected when six U-boats intercepted SC 7 west of Rockall Bank (northwest of the British Isles) on Oct. 16, 1940. The convoy of 34 ships was protected by escorts, including three of the RN’s new Flower-class corvettes—the kind the RCN was now building as its main auxiliary vessel. The convoy also enjoyed support from a long-range aircraft of the RAF. In fact, U-48, which made the initial contact and immediately sank two ships, was later driven off by the aircraft. Dönitz hurriedly assembled a pack in front of SC 7, and the next night it attacked. What followed was something akin to a shark feeding frenzy: even the Germans had trouble figuring out who did what as five U-boats roamed through the convoy at will. Three of the attackers reported firing all their torpedoes in one night of furious action. By the time it was over 22 ships had gone down: the highest loss rate from any North Atlantic convoy during the war. On Oct. 20, a new pack of five—some from the SC 7 battle—fell on HX 79, screened by no less than 11 escorts, including two destroyers and three corvettes, and sank a further 12 ships. For the moment there seemed to be no clear solution to the new German U-boat tactics, and the assault had only just begun.

Although there was no Canadian involvement in the battles around SC 7 and HX 79, RCN destroyers operating from British bases were deeply involved in this early phase of the battle with the wolf packs. They and their struggling RN companions would need new equipment, organization, leadership and training to cope with the wolf packs. And they would need help. By the fall of 1940, British corvettes were already battling U-boats in the broad ocean, and Canadian-built versions were just starting to appear. Trillium, the first to complete at Vickers yard in Montreal, commissioned on Oct. 22—the day the battle for HX 79 ended. Windflower commissioned four days later, six more commissioned in November and three more in December before ice closed the St. Lawrence. Canada’s wartime construction programs were starting to bear fruit just in time.

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