VADM Sagerholm is a retired submarine officer. He comma11ded USS KAMEHAMEHA (SSBN642) a11d was Deputy Director of Naval Intelligence. As a Flag Officer he served as Commander, south Atlantic Force a11d as Commander, Naval Education and Training.
In Part I, VA DM Sagerholm set the stage Jo,. the actual operations of the Battle of the Atlantic, a11d the big picture strategic question posed by tire title. He outlined the back-ground for the force structure, and tactics, both sides !tad at the start of the War i11 September of 1939. He also noted the advantages and disadva11tages of that force structure, the productio11 problems i11lrerent in starti11g a complex construction program after a significant hiatus, and the practical difficulties of resource allocation between services in the face of a national leadership lacking a sufficiently sophisticated overall program for achieving its wartime goals.
Two questions at the start of Part I are based 011 World War 1 German experience and form a major point in getting to the a11swer posed by tire title. Admiral Sagerholm asked why Kaiser Wilhelm failed to recog11ize the lesson of history when, in the lead-up to WWI, he built his High Seas Fleet to be second only to Britain’s. He also asked wiry the WWI experience of early success and near victory in the submarine war, followed by total defeat, was repeated in WWII; given that Germany ” … arguably possessed the most experienced submariners of any navy in the world.”
Donitz was firmly wedded to the idea of employing group tactics as the means to defeat the convoy system. In the winter of 1938-1939, he had conducted an open ocean exercise in the Atlantic for the purpose of testing the concept, including command and control, locating convoys, and bringing U-boats to the convoy for group attack. Analysis of the exercise convinced him that group tactics could be decisively successful. However, numbers assumed critical importance, and it was from the analysis of this exercise that his requirement for 300 submarines was derived.
When forced to commence the submarine anti-shipping campaign with but 22 boats on 3 September 1939, Donitz resolved nevertheless to try group tactics at the first opportunity. To this end, he assembled in October 1939 a group of six U-boats under the tactical command of Senior Officer Sixth U-Boat Flotilla in U-37, with the intent to have the group operate at the convergence point for shipping entering the Straits of Gibraltar. U-40 was late getting to sea and, while traveling the shorter route through the English Channel, struck a mine and was lost. Two other boats, U-42 and U-45, were lost to destroyer attacks while passing west of Ireland. The remaining three encountered a convoy west of Portugal and attacked. Three to four ships were estimated to have been sunk, but in the attack, one of the U-boats expended all of its torpedoes and had to return home. The last two boats then proceeded to separate patrol areas for independent operations, ending any attempt at group tactics.
The first wolf-pack operation had hardly been an outstanding success, and showed that numbers were indeed necessary in order to account for losses that might occur as well as to provide a broader coverage of the ocean to facilitate locating convoys. The operation also con firmed the in feasibility of trying to exercise tactical control from one of the boats in the group.
The officer in tactical command had necessarily to be surfaced, and thus had to stand off at a distance from the action, making his ability to control the attack nearly nil. A second attempt in early November produced results similar to the first attempt; Donitz therefore reverted to ordering independent operations until sufficient numbers of boats were available. It would be another eight months before wolf-pack operations were again attempted.
Donitz chose to extrapolate the tenuous results achieved with just a few boats into the conviction that group tactics had been verified as the key to successfully countering the convoy system. He resolved the question of controlling the group’s concentration against a convoy, once located, by determining that he could do so by radio from his headquarters ashore, using sighting reports from U-boats as well as intelligence obtained from the German code-brcaking group, B-dienst. Once the boats were assembled in attack positions, each boat was released to act independently, the success or failure of the attacks being determined by the skill and dash exercised by the individual skipper. Following the action, Donitz required each commanding officer to submit an after-action report to him personally and in detail. To one accustomed to submarine operations where silence is the key to initial surprise and ultimate survival, the numerous broadcasts required of the U-boats appears to have been a ready formula for their loss, but Donitz maintained that the use of short code signals denied the enemy any precise direction finding ability, and thus he argued that his requirements posed little risk to his boats II This was just one of several erroneous assumptions made by Admiral Donitz regarding the ability of Allied forces to locate his submarines.
One of the consequences of convoying by the Allies was the removal of ships from most of the ocean, the ships now being concentrated in the convoys. This significantly increased the difficulty of locating ships lo attack in the broad reaches of the ocean. One course available to the U-boats was to gather at or near points of convergence of sea routes where convoys or ships had to transit in order to arrive at a given destination, points such as the Straits of Gibraltar or the area just northwest of Ireland. This approach worked well in the early years of the war when the British anti-submarine resources were still thinly stretched. During one episode in September 1940, while operating between Rockall Bank and the North Channel, the U-boat aces Prien, Kretschmer, Schepke, and Bleichrodt sank nineteen ships and damaged three others, in action lasting less than a week. However, the Allies were of course aware of this vulnerability, and when forces became available later in the war, the concentration of surface and air coverage at such points was increased, forcing the relocation of U-boats to the west in the open Atlantic. Under these conditions, instead of random searches by individual U-boats, an alternative was devised wherein the U-boats extended a line across an area of the ocean where a convoy bound for Britain from America was expected to pass, based upon information provided by B-dienst. When a boat sighted a convoy, an immediate report was made to headquarters, and boats in the area were vectored to the location reported. The success of this approach depended heavily upon sea and weather conditions. A convoy might or might not be sighted as it passed through the U-boat line. The bridge of a surfaced boat was less than twenty feet above the waterline, allowing a field of vision of less than ten miles in radius on a clear day, and much reduced in poor weather or rough seas. Germany was slow in developing radar, so passive sonar was the only sensor available for detecting a convoy, and although German passive sonar was excellent, sonar performance depended on water salinity, water temperature layers, and sea state, all of which affected sound transmission in the sea.
A related factor affecting the ability of U-boats to intercept convoys was the work being done by the Allied signals intelligence analysts. When the Allied code-breakers intercepted and decoded orders to the U-boats, the convoy commodore was advised to change to a new course specified in the message without any reference as to why.34 While this may seem to be a relatively straight-forward process wherein the intercepted message is decoded, analyzed for its effect on a convoy, and then suitable warning given to the convoy commander, in reality the process was far more complicated and subject to a number of variables, not the least of which was the ability of the decoders to actually break the message in all its parts in a sufficiently short period of time to be useful, usually less than 48 hours, and having done so, for the analysts to understand properly its import. The Allied system for decryption of intercepted transmissions was known as Ultra, which was part of the broader area of signals intelligence (sigint) that comprised any use of intercepted electro-magnetic emissions made by the enemy. Ultra was the product initially of a group of crypt analysts working in Britain at Bletchley Park, an estate in the countryside near Oxford. There, in near total isolation from the rest of the world, mathematicians and electronics experts worked together in the effort to unravel the mystery of the German Enigma machine, the device used by the Germans to encode and decode their encrypted messages. Employing a system of three (later four) rotors containing letters and numbers in different sequences, rotating in accordance with a series of settings that changed either at random intervals or at regular times, depending on the user, and thus creating millions of possible combinations for any letter or number to be encoded, the system was deemed to be unbreakable by the German cryptology community. However, unknown to the Germans, an Enigma machine had been recovered from a U-boat before it sank, together with some of the code books. With these as a start, as well as the invaluable assistance of three young Polish engineers who had escaped from Europe with significant information regarding the system, a primitive computer using vacuum tubes was built to run the vast number of combinations to be tested that ultimately led to decryption of messages using the Enigma system. While Ultra was of considerable aid in countering the U-boat threat, it was but one of several aids derived from sigint, one being traffic analysis, which is the statistical analysis of transmissions to determine patterns from which information may be deduced; another being high-frequency direction-finding, HF/DF, of which more later.
At one point in the Battle of the Atlantic, the Germans added a fourth rotor to the Enigma machine, which totally denied the Allies the ability to decode Enigma traffic, a situation that lasted for some four months until the combined efforts of the cryptanalysts at Bletchley Park and at the National Cash Register plant in Dayton, Ohio worked out the algorithms needed to once again read the German messages. In the employment of Ultra, extreme care had to be taken in making use of the information so as to avoid revealing to the Germans what was being accomplished. As it was, Donitz several times questioned his signals intelligence agency, B-dicnst, as to whether the Allies were breaking the Enigma mes-sages, his suspicions aroused by convoys seemingly disappearing from projected routes after his boats had been advised of intercept points to take. He was assured that the millions of combinations possible in Enigma encoding made it impossible to decode their messages. And so it would have been but for the building of the primitive computers that were able to run the necessary thousands of computations that were needed to break the codes. Having been so confidently assured by B-dienst of the security of messages to the U-boats, Donitz and his staff concluded that the cause of convoy re-routing was the locating of U-boats by very long-range airborne radar combined with deductive analysis by the British based on information provided them by French underground intelligence networks. His own B-dienst was breaking British reports of U-boat locations being broadcast to the convoys and hunter-killer groups at sea in the Atlantic, and were a source of information for the U-boat command of which the British were unaware, but B-dienst never accepted the possibility that the British ability to identify U -boat locations was the result of decoding German message traffic. So the game of cat and mouse switched back and forth throughout the wa r, and at the time of the writing of his memoirs in 1957, Donitz was still “not certain whether or not the enemy did succeed in breaking our ciphers during the war.”
A third method for locating convoys was aerial reconnaissance, a method that intuitively offered the most efficient means with its relatively rapid coverage of large areas of the ocean. However, there was no naval air arm, so any air reconnaissance required the cooperation of the Luftwaffe. When Donitz approached Reichsmarschall Hermann Goring following the fall of France, Goring refused to provide any assistance, citing the needs of the Luftwaffe in the ongoing battle to subdue Britain by air attacks. Donitz then took his request to Hitler who, on 7 January 1941, ordered Air Group 40 in Bordeaux to be placed under command of the navy. However, the Fw200 aircraft that comprised Air Group 40, although considered long range by the Luftwaffe, did not have the range needed to cover the western Atlantic, and were therefore restricted to sweeps over the Bay of Biscay to the Straits of Gibraltar and as far north as the North Channel above Scotland. Although the Fw200s eventually provided successful reconnaissance in the Gibraltar area, the shipping entering the Mediterranean was mostly of smaller tonnage than the ships headed for Britain. Furthermore, the supplies going to Britain were the prime target, but the Fw200, being a converted domestic airliner, simply was unable to effectively operate in the much more hostile environment of the north, hostile both from enemy aircraft and from weather conditions at those latitudes. By the end of 194 l, therefore, Donitz concluded that Air Group 40, despite the efforts of the aircrews, was not equipped to answer the needs of the U-boat service. The problem of locating convoys in the open ocean, once the shipping convergence points were denied to the Germans, remained a problem for the rest of the war. Donitz concluded that the ” problem could only be solved by the acquisition of more boats,” but it was not until 1943 that he had even a force of 100 boats, let alone the 300 that he had identified as needed, and by 1943, the tide of battle in the Atlantic had turned against the U-boats.
From the very outset of its restoration in 1935, the U-boat arm was never given the recognition it deserved as a critical element in Germany’s war against first Britain, and then against Britain and the United States. Hitler and his generals, together with Reichsmarschall Goring, were co11tillenta/ in their focus, and failed to appreciate that the winning of the war required the defeat of Britain, which in turn required that Britain be denied the means to wage war. The effects of this were felt throughout the war, and included difficulty in competing for materials and personnel for U-boat construction and maintenance, lack of air support, redirection of U-boats from the Atlantic to the Mediterranean in support of the Africa Korps, a similar redirection to Norway during the invasion by Germany, and the lack of sufficient priority for the development of countermeasures to offset Allied innovations in anti-submarine warfare.
The relationship between Grand Admiral Erich Raeder and Admiral Donitz was initially marked by a conflict as to the course a rejuvenated navy should take. Raeder had been head of the navy since 1928, and steered it through the turbulent times of the Weimar Republic, and on into the rise and takeover of the country by the National Socialists led by Adolf Hitler. Raeder had been impressed by Hitler’ s ability to out-negotiate and bluff the British and French. He therefore accepted Hitler’s word that there would be no war for at least a decade, and set the date of 1948 for completion of the navy’s reconstruction. Subsequently, at Hitler’s direction, the completion date was moved up to 1944, a move that should have alerted Raeder that Hitler’s intentions were such that he expected to have war earlier than he had previously indicated to his generals and admirals. Raeder’s goal was the creation of a balanced fleet of battleships, aircraft carriers, cruisers, destroyers, and submarines, a fleet capable of open ocean operations in the Atlantic. Donitz, who had been appointed by Raeder to the post of Senior Officer, U-boats in 1935, saw the future of the German Navy primarily as a commerce destroyer using submarines as the principal force. The disagreement on the future of the navy had the unfortunate effect of delaying the submarine building program. Once war started, however, Raeder had been persuaded of the need for a strong U-boat force. He scrapped the balanced force plan and argued for increased production and support of the submarine force, but he failed to convince Hitler, who evidently never grasped the importance of the U-boat campaign to the overall war effort. It was at th is time that Raeder, as commander-in-chief of the navy, should have pressed Hitler and Goring for the creation of a joint Atlantic command to coordinate air and sea assets in the campaign to stop or significantly reduce the flow of war materials and food to Britain. Such a command would have been especially useful when the need for aerial reconnaissance was critical to the success of wolf-pack tactics. Both Raeder and Donitz saw Hitler as being so deeply committed to land warfare that his understanding of Wcltmacht in a Mahanian sense was hopelessly warped. Although Raeder had trouble from time to time with what he viewed as Donitz’s excessive ego and stubbornness, he nevertheless also appreciated the latter’s abilities and expertise in submarine warfare, and continued to support him and the U-boat arm until Raeder’s retirement in 1943.39 Nevertheless, Raeder’s pre-war faith in Hitler’s ability to avoid war through negotiations had led Raeder to accept Hitler’s assurances that there would be time to complete the navy’s building plan before any war might be expected. As a result, when war actually erupted in 1939, the navy in general, and the U-boat force in particular, were well below the numbers calculated as needed to attain the goal of destroying British shipping to the extent necessary to bring about Britain’ s defeat.
German technology did not live up to its reputation when it came to support of the U-boat campaign. Torpedo detonators were not properly tested and resulted in numerous failures in the first two years of the war. The German electronics experts lagged behind the Allies throughout the war in the development of radar, and showed a poor understanding of the use of microwave radar, claiming that it was impossible to use frequencies in that range, yet U-boats were being attacked in pitch darkness by aircraft appearing seemingly from nowhere. It was not until a British bomber carrying centimetric radar was recovered in Holland that the German scientists were confronted with hard evidence th at such radar not only existed, it was capable of discerning small objects at ranges deemed impossi hie by the Germans. Initially, the U-boats were provided a radar detection device named Metox, that being the French company that manufactured it. The system came with a primitive makeshift antenna consisting of a wooden cross with a wire stretched around it, connected to a cable that led down through the bridge hatch into the conning tower, an arrangement that had to be rigged every time the boat surfaced, and unrigged whenever the boat submerged. The crude antenna was limited to detections at such short range that when the device emitted the radar detection signal, the source of the signal was so close that the boat had to crash dive, but first the antenna and cable had to be stowed below, a clumsy and dangerous arrangement. Eventually, the boats were fitted with circular metal antennae that were much more sensitive and were permanently mounted on the bridge.
Later innovations that looked promising on the drawing board did not meet expectations. One such was the anti-escort acoustic torpedo that was designed to home on the screw noise of destroyers and other smaller escorts. While these torpedoes initially were successful, the Allies quickly devised acoustic countermeasures that decoyed the torpedo, rendering it harmless. However, the early success of the acoustic torpedoes, together with the new circular antennae and a new radar detector named Wanze, instilled a false sense of confidence in the boats so equipped. Wanze detected the same low to medium frequency radars as Metox but at much greater ranges from the emitter, allowing adequate time for evasion. Boats also now had their own radar for use against night attacks by aircraft and for night surface attacks against convoys. This new· found confidence was short-lived, however, when a night wolf-pack attack against a convoy was thwarted by the sudden and undetected attack of aircraft appearing out of nowhere in the pitch-black night. No Wanze warning had been given, and the low altitude approach by the aircraft was not seen on radar until the aircraft was bearing in on the boats. It was evident that aircraft were using radar of a frequency not detectable by the Wanze, the higher frequency centimetric radar.
Even the much touted Type XXI and Type XXIII boats that were introduced near the end of the war, while indeed capable of high underwater speeds attributed to their hull design and their greatly increased battery power, were found to be sloppily con· strutted, and experienced hull cracks and joint leaks when subjected to shock tests.
Although B-dienst continued to provide information on convoy routes, the ability of the U-boat force to exploit the information was increasingly impeded by the continual Allied innovations in technology, tactics, and types of forces.
It is important to recognize that the convoy system was the foundation upon which the Allied anti-submarine effort rested. The convoy system provided a structure that fully was in consonance with the primary objective of the Allies in the Battle of the Atlantic, namely, the arrival intact of ships and their cargoes at whatever destination was intended, be it North Africa or Britain or Murmansk. There were several ways to accomplish the mission of getting the cargoes to where they were needed. One way was to avoid the threat by selective routing of the convoys based upon knowledge of the location of the U-boats; another was to attack the U-boats when they approached a convoy, ideally before the boats could attack and in the process either destroy them or repulse them. In practice, both methods were used.
The first method required intelligence as to the location and intentions of boats at sea, intelligence obtained from the Ultra process previously described. Any transmissions from the boats that provided detection opportunities for HF/DF were more valuable in a real-time sense. HF/DF was a system where individual stations intercepted the same signal but at different locations, thereby obtaining a set of bearings of the signal which, when plotted on a chart, intersected at or near the location of the transmitter. It was the combination of Ultra and HF/DF that enabled Allied convoys to be redirected so as to avoid U-boats. It was also the installation of HF/DF on escorts and escort carriers that allowed a rapid reaction of a convoy’s protective force to strike at the U-boats before the latter could reach their intended attack position.4 3 Despite the growing evidence of the effectiveness of HFIDF in countering the U-boat threat, Donitz doggedly clung to the notion that the accuracy of the bearings was so poor that HF/ DF mounted no significant threat to his force. In addition, he asserted that the use of “spurt” transmissions denied the direction finders the ability to determine a bearing or even to detect the transmission.44 By the autumn of 1944, U-boat captains had no such illusions about HF/OF, and “were generally averse-and rightly so-to using their radios and were apt to give up after one or two abortive attempts to pass a message; in fact, the more cautious of them made no attempt at all.
In neither OKM nor in the U-boat command was there a well-dcvcloped and realistic strategy for the employment of the ships and submarines of the Kriegsmarine in the event of war with Britain and France, the n’tost likely adversaries of Germany.
Raeder and OKM were seized with the potential problem of breaking a British blockade, the same problem the German Navy faced in World War I. In the latter instance, the German High Sea Fleet had been unsuccessful as an opponent of the Royal Navy, and although it claimed a tactical victory at the battle of Jutland, it failed in its strategic objective of breaking the British blockade. Hence, it had resorted to a counter-strategy of submarine warfare against British shipping, a course that eventually led to the entry of America into the war, with the consequent defeat of Germany. Hampering OKM in its planning was the Hitler postulate that Britain would maintain a be11evo/e11t 11e11trality if a war on the continent were to occur. Nevertheless, Raeder’s strategic vision called for a German Navy capable of operating in the open reaches of the Atlantic, a navy consisting of 365 ships by 1944, including six battleships, four aircraft carriers, twelve heavy cruisers, and 233 U-bonts, a balanced fleet that would in his eyes be capable of successfully challenging the Royal Navy.
Raeder’s vision of challenging Britain on the high seas consti-tuted a strategic disconnect with the grand strategy of Nazi Germany. It was a maritime strategy at odds with Hitler’s policy of avoiding war with Britain, and did not support Hitler’s continental goals of German territorial expansion to the south and cast. Furthermore, it disregarded Germany’s geographical position that found movement by sea to the Atlantic impeded by the natural barrier of the British Isles. Raeder recognized the need for making the most effective use of his forces by hitting the enemy’s most vulnerable points, and he further saw the need for joint operations with the army and the Luftwaffe.47 In the event, however, Raeder failed to attain his fleet due to the early onset of war with Britain; failed to economize the use of his limited numbers by concentrating the U-boat force on striking Britain’s most critical sea lines, its transport of oil from the Persian Gulf and the Caribbean; and failed to have established a joint air-sea command for coordination of Luftwaffe assets with naval assets. It should be noted that Hitler was not consistent in formulating naval policy, approving on the one hand the expansion of the fleet and insisting that it be second to 11011e, while on the other hand committing top priority to the army and air force in support of his continental ambitions of cxpansion.48 The inability of Hitler to understand the role of sea power in a comprehensive grand strategy was critical to the outcome of the Battle of the Atlantic and of the war. The Battle of the Atlantic should have been seen as a necessary part of the overall schema for winning the war, since so long as Britain remained as an opponent, the war could not be won.
The strategy adopted by Donitz was not in consonance with Raeder’s original plans, calling as it did for a navy dominated by the U-boat force, nor was it more than an adaptation of the World War I U-boat war against commerce, the only innovation being the use of wolf-packs, a tactic that required large numbers of U-boats in order to be implemented properly. As it was, Donitz had less than one-tenth of the ocean-going boats he needed when hostilities commenced, but neither he nor OKM made any strategic or tactical adjustment to accommodate his lack of numbers, despite Raeder’s previous acknowledgement of the need to maximize the effective-ness of forces inferior in numbers.
In the period between the world wars, the international naval community had accepted the British claim that ASDIC, the acronym used for shipborne underwater sound listening devices, had attained the capability to locate and track submarines such that the threat of the latter had been nullified. However, when put to the test once hostilities commenced, the claim was found to be excessively exaggerated, and the locating and tracking of a submarine maneuvering to avoid being tracked proved to be a daunting task, requiring a high degree of skill by the operator together with a fair amount of luck. Maximum detection range was usually about 2000 yards, or one nautical mile, well within the range of torpedoes. When depth charges were dropped, the explosions obviously blocked out any other sounds, a condition that lasted long enough to cause contact to be lost. This disadvantage was overcome by the development of search tactics involving at least two cooperating escorts, one of whom maintained a position at the last known location while the other(s) conducted an expand-ing square sweep that moved away from the target datum and covered the possible escape routes of a slow moving submarine. If the submarine elected to stay in the reverberation area, the station-ary escort was in position to regain contact when the noise level subsided sufficiently. The later development of the hedgehog ahead-thrown small charge launcher allowed an escort to fire fourteen projectiles simultaneously in a circular pattern with a diameter of a hundred yards or so at a distance of several hundred yards ahead of the escort. The charges detonated only on contact with the hull of the submarine, thus indicating the range and direction of travel of the submarine as well as considerably reducing the sound interference with the sonar.
Augmenting the development of weapons and improvements in sonar was the formation of the Anti-Submarine Warfare Operations Research Group (ASWORG) in April 1942, comprised of civilian scientists and naval officers working together to address such problems as the most effective tactics to regain contact, the most efficient use of aircraft in covering a convoy, and similar problems encountered by the forces fighting the U-boats. Working at sea with the ships and aircraft of the Tenth Fleet in the North Atlantic and the Fourth Fleet in southern waters, ASWORG determined for example that three destroyers searching in line abreast were more than three times as effective as a single destroyer. They developed box searches and the expanding square search for regaining contact. Aircraft search speed, altitude and patterns for most effective coverage of an ocean area were developed.51 These were but several of the contributions made by this group to the Battle of the Atlantic. By contrast, neither OKM nor Admiral Donitz attempted the use of similar talent in Germany.
A major contribution of Anglo-American technology was radar, both shipborne and airborne. Invented in Britain before World War II, with improvements by American engineers, radar was installed on Navy vessels in 1942, providing a search radius at least five times farther than lookouts could provide in clear weather, and radar had the added advantage of seeing through areas of low visibility. The addition of radar to aircraft was especially of value in covering large areas of ocean in sweeps by the long-range land-based B-24 Liberators and B-17s assigned by the Army Air Force to ASW patrols over the North Atlantic, as well as the growing fleet of Navy patrol aircraft. Again, this example of inter-service cooperation stands in marked contrast to the refusal of Goring to assist the U-boat force in its campaign. As has already been noted, the eventual use of centimetric radar by aircraft proved to be especially effective in permitting the aircraft to surprise a boat on the surface, usually with the resultant loss of the boat.
