U-3008 (Type XXI U-Boat) at Wilhelmshaven, June 1945. Note the two type IX submarines to its left. U-3008 was one of only two type XXIs to make a wartime patrol
The most likely reason why Hitler chose to defend Courland and other bridgeheads along the Baltic concerns the Atlantic Ocean more than the Eastern Front. It is well known that the Luftwaffe suffered a serious defeat over Britain in the second half of 1940. Historians also acknowledge that the German army met its match at Moscow in December 1941 and that it never regained the strategic initiative after the Stalingrad debacle the following winter. Yet people often forget that the tide did not turn against German navy until May 1943. Following the defeat in the Battle of the Atlantic, Dönitz’s single-minded goal was to regain the initiative in the war at sea. He planned to achieve this with new models of technologically advanced submarines that would sever the link between the Old World and the New, isolating America and starving Britain into submission. But first these new U-boats had to undergo trials and their crews had to be trained, both of which for geographic reasons were possible only in the eastern and central Baltic. It was absolutely essential to Dönitz to control the Baltic so he could ready his new submarine force for operations in the Atlantic.
Although the German navy had been woefully unprepared for war in 1939, Dönitz’s U-boat arm increased in size and efficiency. The number of submarines in the first year of the war hovered between fifty and sixty. This number increased dramatically to 248 commissioned U-boats in January 1942 and 400 in January 1943. The year 1942 was a banner one for German submarines. Following Hitler’s declaration of war on the United States, U-boats prowled off America’s East Coast and in the Caribbean, sinking so many Allied vessels that the period from February to October 1942 became known to German submariners as the “Happy Times.” When American antisubmarine defenses improved, Dönitz shifted his U-boats back to the North Atlantic, where they again achieved impressive results. After a slow start in the first two months of 1943, large numbers of German submarines put to sea. The critical months of March through May saw the climax of the Battle of the Atlantic. Rarely has a period of victory been so closely followed by one of utter defeat. The Naval Staff (Seekriegsleitung) Skl announced that in March 1943 U-boats had sunk 140 ships of some 875,000 tons for the loss of 14 submarines. Near the end of the month Dönitz’s submariners claimed to have fought their most successful convoy battle of the war, sinking a destroyer and thirty-four merchantmen of 200,000 tons without losing any of the thirty-eight attacking U-boats.
Yet trouble was on the horizon. Dönitz met with Hitler in mid-April 1943 and reported on rising submarine losses in the Atlantic. Germany had lost nineteen U-boats in February, fifteen in March, and six during the first ten days of April. The advent of more effective Allied antisubmarine measures, he declared, called for increased U-boat construction. Dönitz proposed that the goal be increased from the as yet unreached figure of twenty-five submarines monthly to thirty, and Hitler agreed. In May the Germans claimed to have sunk fifty-seven ships of 344,000 tons, but at the cost of thirty-eight U-boats. Dönitz concluded that losses had reached an unacceptable level and ordered his submarines to leave the North Atlantic. Twice that month Dönitz briefed Hitler on the crisis of the U-boat war. He explained that Allied air superiority, coupled with a new device that enabled aircraft to locate submarines even during conditions of poor visibility, had deprived the U-boat of its advantages of stealth and surprise. Dönitz insisted that current losses made yet another increase in submarine production necessary and secured Hitler’s consent to raise production to forty U-boats per month. To expedite this, Dönitz asked that the armaments minister, Albert Speer, take over all naval construction, and Hitler approved this measure on 31 May.
Dönitz planned to regain the initiative in the war at sea with two new models of submarines, the Types XXI and XXIII. The Type XXI, intended for action in the Atlantic, had a crew of fifty-seven, was 237 feet long, weighed 1,600 tons, and could maintain a submerged speed of eighteen knots for and hour and a half, or twelve to fourteen knots for ten hours. This speed and endurance signified a tremendous improvement over existing U-boats, which traveled underwater at six knots for forty-five minutes, at best. Most Allied convoys sailed at speeds of six to nine knots; the new submarines would be able to approach convoys and escape pursuit much more easily. Furthermore, the addition of a “silent running” motor for speeds up to five knots would make detection by listening devices much more difficult. The Type XXI’s design also incorporated additional defensive and offensive improvements. Thicker hull plating rendered the submarines less susceptible to damage from depth charges, and improved listening and location devices permitted submerged attack without the use of the periscope. These U-boats were also called “electro-submarines,” because of their two 2,500-horsepower electric motors.
The idea for the Type XXI had originated at a conference Dönitz held in Paris in November 1942 with U-boat engineers and representatives from the Naval Construction Office. The designs for these submarines, completed in June 1943, combined the streamlined hull form of the Walter submarine (discussed below) with conventional means of propulsion. With its larger hull the Type XXI had two to three times the battery capacity of existing U-boats, which greatly enhanced its submerged speed and endurance. This submarine could also dive deeper than current U-boats; it was capable of reaching 376 feet, compared to 309 feet for the Type VII-C.6 The Type XXI had six bow torpedo tubes and could fire eighteen of its twenty torpedoes in twenty to thirty minutes. The smaller Type XXIII, intended for use off Britain’s coast and in the Mediterranean and Black seas, had a crew of only fourteen, was 114 feet long, weighed about 250 tons, and could cruise underwater at twelve and a half knots for one hour. The Type XXIII’s maximum diving depth was 330 feet. One disadvantage of its small size, upon which Dönitz insisted so it could be transported by rail, was that it carried only two torpedoes.
In July 1943 Dönitz enthusiastically reported to Hitler that with their ability to approach convoys and evade pursuit at high speed, the new submarines would render current antisubmarine vessels obsolete, because Allied sub chasers were designed to combat U-boats with slow underwater speed. Furthermore, a submerged speed of eighteen to nineteen knots provided an advantage that would persist for quite some time, since the Allies could not increase convoy speeds to much more than ten knots. The electro-submarines had defensive advantages as well. Dönitz explained that the new submarines could dive faster if attacked and quickly pass through dangerous coastal areas en route to and from operating zones. Intensely interested, Hitler queried Dönitz on a number of the new U-boats’ technical aspects and agreed that they signified a revolutionary development. Hitler asked when the first of these submarines would be ready; Dönitz replied that because the Naval Construction Office’s estimate of November 1944 was too late, he had requested Speer, who was present, to devise a method to accelerate production. Hitler turned to Speer and instructed him to give construction of these U-boats top priority.
Dönitz also briefed Hitler on recent developments in the U-boat war. He reported that a professor at IG Farben believed he could develop a material to absorb radar waves. He announced also that he planned to return to the North Atlantic once a new antidestroyer torpedo was ready. Finally, he requested additional manpower for his branch of service; Hitler replied that he was devoted to the navy and would do everything he could for it.
In hopes of regaining the initiative in the U-boat war, in mid-August Dönitz ordered submarine construction shifted to the new types XXI and XXIII. Despite this changeover, he insisted on a steady monthly output of forty submarines. Speer had reexamined initial delivery estimates and promised the first Type XXI in April 1944. To expedite their availability, Speer built these new submarines in a radically new fashion. His biggest gamble was to rush the submarines into production straight from the design stage, without first building a prototype. To ensure a smooth transition to the new building program Speer established a Central Board for Ship Construction in the summer of 1943. This committee consisted of representatives from the navy and the Armaments Ministry; it was headed by Otto Merker, whose previous experience was in the automobile industry. To reduce the amount of time and the number of workers required to build the U-boats, Merker proposed building the new submarines in prefabricated sections to be fitted together according to assembly-line procedures. Over a thousand designers and engineers worked at a central design agency in Blankenburg, in the Harz Mountains, to draw up the final plans for the new U-boats. Naval Construction Director Heinrich Oelfken headed this organization, the Glückauf Construction Office. Naval engineers concluded that building the Type XXI in eight sections would cut construction time from at least twenty-two months to as little as five to nine months. In addition, early estimates revealed that sectional construction would reduce slip time by 50 percent, a matter of vital importance, because submarines were particularly vulnerable to air raids while on slips.
Industry throughout the Reich produced submarine engines and accessories, and thirty-two inland factories built the prefabricated sections. From these factories the sections, weighing up to 150 tons and thus too heavy for rail transport, proceeded via inland waterways to eleven fitting-out yards near the coast; there they received propellers, engines, periscopes, cables, and other equipment. Finally, the completed sections went to three nearby shipyards—in Danzig, Bremen, and Hamburg—for assembly. Dönitz placed orders for 170 Type XXI and 140 Type XXIII U-boats in the fall of 1943.
The Germans planned to transfer final assembly of the new submarines from vulnerable shipyards to a colossal bombproof plant. Work on this facility, located on the Weser River near Bremen, began in early 1943 and was still in progress at the end of the war. The complex was approximately 1,350 feet long, 380 feet wide, and 75 feet high, with reinforced concrete walls nine to thirteen meters thick and a roof twenty-two feet thick. The building would accommodate twenty-four sections and thirteen or fourteen assembled submarines. The sections were to reach the building on barges traveling up a connecting canal and then to proceed along an assembly line, with finished submarines coming off the line inside the shelter. At the end of the assembly line each U-boat would be launched by flooding a lock chamber. Following engine tests the submarine would leave the plant’s bombproof doors and enter a canal to the river for its journey to the sea. The navy planned the construction of several similar installations. Although never completed, the undertaking of this mammoth plant reveals the expenditure of labor and materials the Germans were willing to make to build these U-boats.
Yet even the formidable Type XXIs and XXIIIs represented only an intermediate stage in German submarine development. Dönitz intended the “electro” U-boats to carry on the fight while the navy perfected a still more advanced weapon, the Walter U-boat. In the early 1930s engineer Hellmuth Walter had devised plans for a high-speed, lightweight submarine with a streamlined shape and an engine that used hydrogen peroxide fuel, which would eliminate altogether the need to surface. In 1939 he received a contract to build an experimental submarine. Walter built an eighty-ton unit, and during its trials in 1940 the Walter U-boat attained an astonishing underwater speed of 28.1 knots. In November 1941 Raeder and Adm. Werner Fuchs, head of the navy’s Construction Office, attended a demonstration of this U-boat. Raeder expressed great interest, though Fuchs’s office was slow to approve further tests. In January 1942 Walter contacted Dönitz, who embraced the idea wholeheartedly and requested development of these submarines as quickly as possible. Yet Fuchs’s office contended that the introduction of a new-type U-boat would impede current production. Dönitz nonetheless continued to push this project, and on 4 January 1943 the navy ordered twenty-four small Walter submarines, designated the Type XVII.
What Dönitz really wanted, however, was an Atlantic U-boat, and Walter began work on a submarine of this type in January 1942. Still the navy was hesitant to develop Walter submarines. Dönitz sent word to Hitler, who called a conference to discuss the Walter submarine on 28 September 1942. Hitler began the meeting by stressing the significance of quickly bringing new weapons into operation. Dönitz seized this opening and declared that existing U-boats required technical improvements to maintain current levels of success in the face of improved Allied antisubmarine tactics. The advantage of a submarine with high underwater speed lay in its ability to approach convoys quickly and elude pursuit. An increase in diving depth would help U-boats evade sonar detection and reduce damage from depth charges. The Walter U-boat was exactly what he needed. Hitler enthusiastically supported Dönitz, which finally put an end to Fuchs’s foot-dragging. Walter presented the drawings for an Atlantic U-boat, designated Type XVIII, to Dönitz in November. Dönitz demanded that the Type XVIII enter production as soon as possible; Walter pointed out that it would take at least a year. Engine installation posed problems for serial production, current manufacture of hydrogen peroxide was minimal, and his engineers wished to await test results from the smaller Type XVIIs and two prototype Type XVIIIs. Hitler expressed keen interest in this project and suggested construction of these U-boats in protected bunkers. By mid-January 1943 Walter had completed revised plans for an Atlantic U-boat. He envisioned the Type XVIII as having a top submerged speed of twenty-four knots, maintained for 270 nautical miles. By the end of the war seven Type XVIIs had been commissioned, but only as experimental and training submarines; they never saw action. The Type XVIIIs were not completed before Germany’s defeat.
To continue the fight until the Type XXI and XXIII submarines became available, then, Dönitz needed stopgap measures. These included improved torpedoes, heavier antiaircraft armament, and the snorkel. More so than earlier, submarines now had to destroy convoy escorts before attacking the merchantmen. The navy was hard at work on an antidestroyer torpedo, which Dönitz hoped to have ready by the end of the summer. On 24 May 1943 Dönitz ordered that all submarines located by aircraft should remain on the surface and engage the enemy with antiaircraft guns unless they could dive to eighty to a hundred meters before the plane released its bombs. This tactic only led to greater losses. By the end of June Dönitz ordered all U-boats to travel underwater through the Bay of Biscay in conditions of poor visibility, although this increased the transit time through this dangerous area. In any event, submarines still had to surface for four to five hours daily to recharge their batteries.
From the latter part of 1942 there were growing indications that the Allies were using airborne radar to locate submarines, yet the Skl virtually ignored this threat until too late. In mid-May 1943 Walter reported he had discovered an effective countermeasure to Allied location systems—U-boats fitted with tubes through which to draw in air and expel exhaust could travel at periscope depth on their diesel engines rather than their electric motors. This would eliminate the need to surface to recharge batteries. Walter pointed out that it was unlikely the Allies could locate so small a device from the air. This apparatus, the snorkel, was not a new invention. When the Nazis overran Holland in May 1940, they had found Dutch submarines fitted with an air mast. The Submarine Acceptance Commission had tested the device, and the Naval Construction Office had suggested trying the snorkel on a submarine in combat, but Dönitz rejected the proposal. When the snorkel finally went into production in 1943, it did so without further tests and with only minor modifications recommended by Walter. A valuable opportunity to evade radar had been squandered in the meantime.
Although the Skl considered location devices the bane of its U-boats, there were actually a number of reasons for the Allied victory in the Atlantic in the spring of 1943. The Allies had recognized the serious threat posed by U-boats and devoted considerable human and material resources to develop effective countermeasures. Unknown to Dönitz, in May 1941 the British had captured a German submarine with its Enigma code machine, complete with instructions. After studying the Enigma machine the Allies were able to decipher messages to and from the U-boats. Knowing the location of submarines allowed the British to reroute convoys and dispatch antisubmarine forces to attack them. The Germans stubbornly believed their codes were unbreakable and made few changes in signals communication. But even the ability to decipher the German Navy’s messages, though it was a key development, alone did not account for the Anglo-American success. Another vital factor was the Allies’ ability to provide air cover over the entire North Atlantic with escort carriers and very-long-range aircraft operating from land. The formation of support groups to hunt U-boats and assist convoys under attack also increased German submarine losses. In addition, the introduction of ten-centimeter-wavelength radar, high-frequency direction finding (HF/DF, or “Huff-Duff”), and new antisubmarine weapons all played key roles. The German obsession with devising countermeasures to radar caused them to ignore the threat from decryption and direction-finding equipment. Although Dönitz blamed Allied aircraft for the turn of the tide in the U-boat war, at least when he was with Hitler, in fact the navy was not blameless, having allowed the enemy to gain the technological lead and failed to make submarine construction a priority.
In the meantime the Battle of the Atlantic continued to go badly for Germany. At the beginning of August 1943 Dönitz reported that the U-boat war would remain costly until the new submarines became available. Hitler acknowledged this but insisted that the war at sea continue to keep Allied vessels engaged in defensive operations. In July the Germans lost twenty-seven U-boats, and the following month thirty-two submarines failed to return, over half the monthly average operating in the Atlantic. At the beginning of 1944 the Skl reviewed the status of the U-boat war. In an attempt to make a steadily deteriorating situation look better, the Skl emphasized that despite the loss of 227 submarines, 1943 had been the second most successful year of the war. Dönitz assured Hitler he would continue the fight until the new models of submarines were ready, pointing out as a problem that the Baltic was the sole training area for the new U-boat force. On 7 January Dönitz abandoned his wolf-pack tactics, ordering submarines instead to operate in groups of three or even individually. Massed attacks against convoys held little promise until the new submarines became operational. This was yet another admission of defeat in the Atlantic.
In January 1944 the Central Board for Ship Construction anticipated the completion of the first three Type XXIs in April and a total of 152 by the end of October. The first two Type XXIIIs were to be delivered in February, and the full complement of 140 by the end of October. The revival of the U-boat war was only a few months away—or so Dönitz led Hitler to believe. He soon had to explain, however, that the new U-boat war would not begin as soon as planned. At the end of February Dönitz reassured Hitler that the new submarines’ high speed would permit them to overtake convoys and that furthermore, since they would operate underwater, the enemy could not detect them as easily, because sonar range was much less than radar. Dönitz added, however, that a recent air raid had seriously damaged the new submarines’ electric motor factory in Berlin, resulting in a two-month delay.
In mid-April Dönitz reported further delays to the Types XXI and XXIII due to bomb damage to an Augsburg factory producing motors. A few weeks later he explained that shipyards in Hamburg, Bremen, and Danzig required additional air defenses, which Hitler ordered Göring to provide. Dönitz also complained that the shortage of workers meant that the navy now expected delivery of only 140, instead of 218, U-boats in 1944; Hitler protested that he had not ordered any reduction in workers for submarine construction. Nevertheless, Dönitz promised, the first Type XXIII would still be ready for action in October 1944.
On 6 June the Allies landed in Normandy, and a few days later Hitler requested a status report on the new submarines. At this time snorkels had been installed on only a handful of U-boats, and these had been sent into the English Channel. Initial reports from snorkel-equipped submarines were encouraging. U-boats fitted with this device had been located by the enemy, but ensuing attacks had been inaccurate. The snorkel seemed the best intermediate measure available until the arrival of the Type XXIs and XXIIIs, now scheduled for the winter of 1944–45. In fact, in the following months the performance of snorkel-equipped U-boats exceeded Dönitz’s initial optimism. The Skl boasted that a submarine had returned from the English Channel after remaining submerged for forty days. Although the U-boats fitted with snorkels did not achieve any spectacular success in the Channel, they were able also to operate off Britain’s east coast, in the Irish Sea, and off Gibraltar, areas into which German submarines had not ventured for three to four years.
The Skl noted with satisfaction that after U-boats had begun to operate solely underwater, losses dropped to the 1941–42 levels. This proved invaluable for boosting U-boat crews’ morale: snorkel travel granted security. But it did so at the cost of mobility, because the time required to journey to and from operational areas increased considerably, due to the slow underwater speed of existing submarines. Although the Germans kept a large number of U-boats at sea, each submarine spent only a fraction of the time at sea actually on patrol. Nonetheless, Dönitz repeatedly emphasized that the snorkel’s success justified his expectations for the electro-submarines, which would perform immeasurably better. The snorkel had proved an effective remedy to air power. With the submarines’ disappearance from the surface, visual search became more effective for the Allies than radar search. Until the end of the war the Anglo-Americans remained unable to produce an effective countermeasure to the snorkel.
On 19 April 1944, the day before Hitler’s birthday, the first Type XXI submarine was launched. U-3501, however, had been launched rather prematurely. Openings in the hull had been patched with wood, and the U-boat returned to dry dock immediately after launching. It was not delivered to the navy until 11 July; it was commissioned on 28 July. The first Type XXI commissioned was U-2501, delivered on 15 June and commissioned on the 28th. Although it had not been launched prematurely, it still required ten days’ work in July to correct faults. The first Type XXIII, U-2321, was launched on 17 April 1944—also too soon; it was commissioned only on 12 June. Prestige, not readiness, was the key criterion for these launching dates. Other new-type submarines followed, although not as quickly as Dönitz had promised Hitler. In the meantime Dönitz’s insistence on continuing the U-boat war exacted a heavy price: Germany lost twenty-seven submarines in July and thirty-three in August 1944. By 1 November a total of thirty-one Type XXIs and sixteen Type XXIIIs had been commissioned. This amounted to but a fraction of the 152 Type XXIs and 140 Type XXIIIs Dönitz had originally planned to have at this time.
Despite this drastic reduction, Dönitz continually promised Hitler that the new U-boat war would soon begin. On 13 October 1944, exactly one week before Hitler ordered Army Group North to defend Courland, Dönitz met with Hitler. He stressed the importance of the Baltic for naval training, adding that he planned to send the first Type XXIIIs into action in January 1945, followed by forty Type XXI Atlantic U-boats in February. Surely Hitler believed that the simultaneous introduction of forty of these new submarines would bring spectacular results. At about the same time Dönitz assured Goebbels that the Type XXI U-boats would sail against enemy convoys in January. On 5 October 1944, however, the Skl had informed the Luftwaffe that the new U-boat war would begin in April 1945. Dönitz was attempting to convince Hitler that the revival of the U-boat war was just around the corner—when he knew that it was not. Submarine construction continued to fall behind even revised estimates. In early September 1944 the navy planned to have 120 Type XXIs and 46 to 50 Type XXIIIs by the end of the year. The actual numbers on 1 January 1945 were sixty-two Type XXIs and twenty-eight Type XXIIIs, despite an increase, achieved by Speer, in total submarine construction in 1944.
At the beginning of 1945 Dönitz reviewed the statistical performance of U-boats per operational day. He concluded that submarines in December 1944 had achieved the same individual rates of success as in August 1942. The substantially lower actual tonnage sunk compared to 1942 resulted from the smaller number of submarines at sea and the increased time required for submerged travel to and from operational areas. This would change, however, with the arrival of the electro-submarines, whose submerged cruising speed was nearly twice that of current U-boats. If existing U-boats could achieve such success, then, stunning victories with the new-type submarines could be anticipated; Dönitz confided to Goebbels that he expected to launch the first convoy battles with the new submarines in February. In mid-February 1945 Dönitz informed Hitler that results from January confirmed this trend. He promised Hitler a sizeable increase in the number of U-boats at sea in the coming months, sixty per month, including the new-type submarines.
Despite Dönitz’s repeated promises that the new U-boat war lay just ahead, it never arrived. By the end of the war fifty-nine to sixty-three Type XXIIIs had been built. Only five or six had put to sea, the first on 29 January 1945 and the last on 4 May. None was sunk while engaged in operations, and Dönitz reported their performance had been excellent. In fact, the biggest problem was that their commanding officers underestimated their speed. They approached too close to their targets, moving so rapidly that they fired the torpedoes within the safety range, inside which they were not armed. The Germans commissioned approximately 120 Type XXI U-boats by the end of the war. Adalbert Schnee’s Type XXI (mentioned in the introduction) left Kiel for Norway on 17 March 1945, but a problem with its periscope postponed operations. On 17 April U-2511 again put to sea, but it had to return four days later due to problems with its diesel engines. Schnee finally sailed on 30 April 1945, just over seven months after U-2511’ s delivery on 29 September 1944. Only one other Type XXI left port in search of enemy vessels. U-3008, commanded by Helmut Manseck, left Wilhelmshaven on 3 May 1945 but, like Schnee’s boat, received Dönitz’s order to cease attacks. Dönitz had based his entire strategy for nearly two years on the deployment of these submarines, and they never fired a shot.
The British and Americans first learned of the new German submarine program in November 1943, and in April 1944 air reconnaissance revealed a “double shock.” Not only were the new-type submarines already under construction, but the use of prefabricated sections made assembly time alarmingly brief. One submarine had been launched after only six weeks’ slip time. Decrypts of signals from the Japanese naval attaché provided the British with detailed information on the Types XXI and XXIII in the spring of 1944. Deciphered messages from the head of the Japanese Naval Mission, Admiral Katsuo Abe, informed the Allies that air raids had delayed the new U-boat offensive until the spring of 1945. This information led to increased bombing raids as well as mining operations in the Baltic to disrupt training. Exact knowledge of these new submarines, however, did not lead to complacency on the part of the Allies. The submerged speed of the Type XXI U-boat was higher than that of Allied corvettes and only slightly slower than frigates. The only vessel that could have effectively dealt with the Type XXI was the destroyer, and the British were chronically short of destroyers. The British Admiralty feared that shipping losses could exceed those from the spring of 1943, and for this reason the British held back approximately three hundred destroyers and escorts originally intended for action in the Pacific.
In addition to the new-type U-boats, other causes for concern existed. The German submarines’ switch to transiting submerged and deploying individually led to a sharp reduction in signaling and thus of Allied decryption. Furthermore, the German Navy had begun experiments in flash transmission of radio messages. Such brief transmissions would have been devastating to Allied high-frequency direction finding as well as to their ability to intercept messages. In view of these developments, the new U-boats could have raised serious problems for the Allies. Churchill’s concern is evident in his request to Stalin at the Yalta Conference in February 1945 that the Soviets capture Danzig (one of three assembly sites for the Type XXIs) as quickly as possible. Signals intelligence provided the Allies with detailed information on U-boat specifications, though estimates on the number of these submarines available were often far from the mark.
When Dönitz had so jubilantly reported to Hitler on the new-type submarines in July 1943, Hitler had declared that it was vital to bring technologically advanced weapons to bear. He had added, however, that technicians must not make exaggerated demands that delayed their availability. Dönitz apparently remembered only Hitler’s enthusiasm. One of the most puzzling questions about these U-boats is why they took so long to become operational. Several reasons account for this. One is certainly that the navy had allowed itself to be surpassed technically, switching much too late to submarines with high submerged speed. Another major cause of delays was damage inflicted by Allied aircraft. Air raids on shipyards caused serious problems, although bombing never halted U-boat construction. Air attacks on German shipyards and assembly yards destroyed and damaged a number of the new submarines as well as essential installations and equipment. Bombing caused greater delays, however, by blocking Germany’s inland waterways; the transport of U-boat sections from inland factories to assembly yards near the coast required passage through a number of canals. Bomb damage to the Kaiser Wilhelm, Mittelland, and Dortmund-Ems canals hampered the delivery of sections. Air raids on factories producing parts for U-boats, particularly batteries and accumulators, were particularly devastating. In addition, the time lost to bomb damage, absenteeism, or simply from workers taking shelter during air raids rose considerably in 1944. Anglo-American aircraft increasingly mined the Baltic to disrupt German shipping and submarine training. Dönitz frequently complained of this to Hitler, claiming that if Germany could not hold open the entrance to the Baltic, the U-boat war would come to naught. On several occasions the Skl noted that U-boat training areas, as well as several shipping lanes in the Baltic, had been closed because of the danger from mines.
Many delays resulted from simple poor planning. The worst example was rushing the submarines into production without a prototype. Inexperience with sectional construction also caused serious problems. The tolerance for fitting sections together (initially plus or minus two millimeters for sections seven meters high and six meters wide) was rarely met, which meant that there was a good bit of shuffling sections around in hopes of finding a better match. Section ends often had to be stretched, shrunk, or patched to obtain a fit. Another problem was that the Type XXI submarines incorporated hydraulic power for all control systems and the periscope, antiaircraft armament, and torpedo hatches. But the Germans were relatively inexperienced with hydraulic design, and defects in the system led to chronic delays. Furthermore, construction of the submarines had already begun when snorkels were added to the design. On several occasions shortages of various components, such as batteries, periscopes, or electric motors, usually caused by Allied bombing, postponed production. Many sections arrived at the assembly yards with essential components missing. Moreover, at this stage of the war Germany lacked many high-quality materials required for these advanced submarines and had to substitute whatever was on hand. Besides shortages of materials, the navy always lacked skilled workers. The Type XXIII submarines did not contain as much highly sophisticated equipment as the XXIs, which accounts for their reaching operational status first. Further, although Hitler had assured Dönitz on 24 September 1943 and again on 26 February 1944 that he would support any measures to accelerate production of the new U-boats, in April 1944 he suddenly granted fighter production top priority. This confusion in armaments production also contributed to delays.
Problems mounted in the final months. The Soviet capture of Danzig in March 1945 robbed Dönitz of one of three assembly sites for the new U-boats. The loss of Upper Silesia denied the navy that area’s industrial output. Chronic shortages of coal and electricity for shipyards, as well as fuel for the submarines themselves, impeded construction and training. A final reason for the Type XXIs’ delay was that each required a long period of trials to rectify teething problems, and their crews needed extensive training. The first Type XXI U-boats built required additional work after commissioning, about six weeks. Recognition of several problems that could be corrected during the construction process later reduced this time to about three weeks. Even proven submarine types normally required four months after commissioning before they were ready for action. The Germans obviously needed more time to work out the bugs in these new submarines and then train the crews. A variety of factors, therefore, contributed to failure of the Type XXI to reach the open seas before the war ended. Postwar studies conducted by the U.S. Navy concluded that had the Type XXIs become operational in large numbers, they could have posed a grave threat indeed.
As it turned out, the Germans had devoted two years and enormous amounts of increasingly scarce raw materials to produce a weapon that did not yield a single Allied casualty. Vast numbers of skilled workers put in a colossal number of hours of labor to build these U-boats, which never fired a single torpedo at an enemy vessel. The construction of each submarine required an average of 252,500 man-hours, and approximately 40,000 production workers were involved in the Type XXI program. The new U-boat program tied up not only thousands of workers and 80 percent of the output of the nation’s entire electrical industry but enormous amounts of steel. The steel for the 170 Type XXI submarines ordered would have provided Guderian 5,100 additional tanks. The German war effort certainly would have benefited more from five thousand tanks than from Dönitz’s “miracle weapon.”