by David Grier
USS U-3008 (ex-German submarine U-3008) at sea, April 1948. (Naval Historical Center)
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.7 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.8
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.9
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.10 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.11 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.12
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.13 Dönitz placed orders for 170 Type XXI and 140 Type XXIII U-boats in the fall of 1943.14
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.15 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.16
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.17 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.18
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.19 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.20 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.21 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.22 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.23
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.24 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.25 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.26
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 1944.27
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 1944–45.28 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.29 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.30
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.31 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.32 This amounted to but a fraction of the 152 Type XXIs and 140 Type XXIIIs Dönitz had originally planned to have at this time.