Hitler’s U-Boat War- The Hunted 1942-45

by Clay Blair

  Admiral King resolved another sensitive issue at Trident. As related, he had sent six fleet boats of American Submarine Squadron 50 to Scotland in December 1942 to augment British submarine ASW patrols. Two of these boats with defective diesels returned to the States, replaced in April 1943 by two others, Haddo and Hake, which also had defective engines. By May 1943, only one of these eight fleet boats had sunk a confirmed ship after about twenty-four war patrols.* Believing the boats to be unsuited for ASW or other missions in European/Arctic waters, on April 20 King had proposed that they be clandestinely employed in special hunter-killer operations against U-tankers, utilizing Enigma decrypts.

  First Sea Lord Pound—and doubtless Churchill as well—had objected to this proposed tactical use of Enigma intelligence, fearing the Germans might realize naval Enigma had been broken. “We should not risk what is so valuable to us,” Pound had cabled. If Enigma “failed us at the present time,” Pound continued in a follow-up cable, “it would, I am sure, result in our shipping losses going up by anything from 50 to 100 percent.”

  King persisted. Off went another cable to Pound:

  While I am equally concerned with you as to security of Zebra [Enigma] information it is my belief that we are not deriving from it fullest value. The refueling submarine is the key to high speed, long range U-boat operations. To deprive the enemy of refuelers would at once decrease the effectiveness and radius of entire U-boat deployment. With careful preparations it seems not unlikely that their destruction might be accomplished without trace. While there is risk of compromise it would be a matter of lasting regret to all if Zebra [Enigma] security were jeopardized in some less worthy cause….

  When Pound again objected to this scheme, King proposed at Trident that owing to the unsuitability of big American submarines for other missions in European waters, Submarine Squadron 50 should be returned to the States and thereafter its six remaining boats be shifted to the Pacific theater. This proposal was approved. Deprived of a job, the squadron commander, Norman S. Ives, took a staff post in London and later was killed by German mortar fire in Normandy during Overlord.

  Historians of the Battle of the Atlantic have slighted or ignored Submarine Squadron 50. And yet, ironically and unintentionally, at the time it made a great contribution to the war, which has only recently come to light in the declassified American Enigma documents.

  For several months in 1943, Allied codebreakers suspected that German code-breakers were reading the combined Anglo-American Naval Cypher Number 3. In view of this possibility, British and American task forces combed through old and current Enigma decrypts for clues. They found a half dozen possibilities, but most cases were too ambiguous and were not sufficiently convincing to set in train a change of codes, a large and complex undertaking.

  While this search was in progress, on May 25, 27, and 31, U-boat Control committed three horrendous breaches of communications security, †

  B-dienst had intercepted and decrypted Allied warnings in Naval Cypher Number 3 to all Allied convoys that three of the Submarine Squadron 50 submarines, Haddo, Hake, and Herring, were to operate at certain positions along the North Atlantic run during their return to the States. Believing that German U-boats in that area should also be warned of these American submarines, Control relayed the Allied information, giving the nearly exact grid squares (latitudes and longitudes) where the three were or were supposed to be, without any exceptional measure to disguise the information with interior codes or by some other means.

  These Enigma decrypts were unequivocal confirmation that, as suspected, B-dienst was reading Naval Cypher Number 3. The discovery assumed added force and urgency because American crews on the three submarines were believed to be at imminent risk. Hence on June 10, Allied communication authorities directed all naval commands and ships to switch to Allied Naval Code Number 5. This switch came as a devastating setback for B-dienst. After months of reading Allied convoy codes with sufficient currency to be of tactical value, in June 1943 German code-breakers suddenly went virtually blind and deaf. In the future they were to regain some Allied convoy codes sporadically, but thanks in large part to the seemingly fruitless patrols of Haddo, Hake, and Herring, the glory days for German code-breakers were over.

  TECHNOLOGICAL REVOLUTIONS AND INTERIM UPGRADES

  By the end of April 1943, the Germans confronted a naval rout in the Atlantic. Allied centimetric-wavelength radar, land- and ship-based Huff Duff, land-based aircraft, skilled surface escort and support groups, Enigma codebreaking, and superb intelligence evaluation and operational-research teams in London and Washington had finally defeated the U-boat force. No existing production U-boat could enter combat in the North Atlantic with even the slightest degree of confidence. Attacks on Allied convoys had become near-suicidal endeavors and would only become more dangerous.

  The defeat of the existing U-boat force was no surprise. Dönitz and U-boat Control had seen it coming for a year or perhaps longer. The increased Allied air power was an important reason, but the “determining factor,” Dönitz explained to Hitler, was “a new [Allied] location device, evidently also used by surface vessels, by means of which planes are now in a position to locate submarines.” That explanation, of course, was only partly correct and it reflected the lack of technological sophistication in Hitler’s Germany, particularly in the Kriegsmarine.

  Both Hitler and Dönitz were in full agreement that the U-boat war must continue. “There can be no talk of a letup in submarine warfare,” Hitler said, according to a stenographer. “The Atlantic is my first line of defense in the West, and even if I have to fight a defensive battle there, that is preferable to waiting to defend myself on the coast of Europe. The enemy forces tied up by our submarine warfare are tremendous, even though the actual losses inflicted by us are no longer great. I cannot afford to release these forces by discontinuing submarine warfare.”

  What was desperately needed was a quantum leap in U-boat technology. That was why Raeder and Dönitz had encouraged and supported the ideas of the inventive engineer Helmut Walter, who had proposed a high-speed, “true” submarine, powered when submerged by engines that obtained oxygen from hydrogen peroxide (code-named “Ingolin”).* As related, Hitler had earlier authorized the construction of two oceangoing Walter prototypes (U-796 and U-797) and twenty-four Walter coastal boats or “ducks” (U-1405 to U-1416; U-1081 to U-1092).

  This radical submarine program, going forward in utmost secrecy, had run into many difficulties. One, ironically, was the overwhelming success of the conventional VIIs and IXs in American waters in the first half of 1942. That heady success, which seemed to portend others, tended to undermine the urgency of the Walter-boat program. Another was the growing number of technical problems. Chief among these was the acute shortage of hydrogen peroxide, which was also used in the V-2 ballistic missile program, likewise under high-priority development. It had become apparent that a big oceangoing Walter U-boat fleet would require several large-scale hydrogen-peroxide production plants for which there were nowhere near sufficient resources. Yet another reason was the intensifying Allied bomber offensive against U-boat building yards. An RAF raid on Kiel on March 12, 1942, had so damaged the first oceangoing Walter test bed, U-791, that it was scrapped.

  It also became apparent that there was a tactical weakness in the hydrogen-peroxide submarine. Unlike conventional storage batteries, which could be recharged for submerged operations (used again and again), hydrogen peroxide was a nonrecyclable power source. Once burned, it was gone. Since there was not enough room in the Walter boat for both a big rechargeable storage battery and hydrogen-peroxide tankage, and that tankage was not, of course, unlimited in size, the submerged endurance of such a boat was restricted. Hence until some means could be devised to replenish this exotic fuel supply at sea (hydrogen-peroxide U-tankers?), the operating radius was quite limited.

  For these reasons and others, by May 1943 it was clear that neither the oceangoing nor the coastal Walter boats powere
d by hydrogen peroxide could be produced in sufficient quantity to influence the outcome of the war. However, Walter came up with another idea that held great promise. The large internal hydrogen-peroxide fuel tanks in the lower half of the figure-eight hull of the large and small Walter boats could be used to add additional storage batteries that could provide about three times the power of those in a VII, IX, or a Type II duck. Wind-tunnel tests and mathematical computations showed that with streamlining and the elimination of deck guns these boats could sprint submerged on batteries at an amazing 18 knots for brief periods. This increase in battery power would give U-boats the ability to overtake and strike convoys at high sprint speed submerged and withdraw at equal sprint speed for several hours, outrunning most surface escorts.

  Owing to the many, many years of R&D invested in the design of the high-speed Walter hydrogen-peroxide boats, it was a relatively simple matter to produce quickly a radically new submarine design, substituting batteries for hydrogen-peroxide tankage. Hence mass production could commence in a matter of mere weeks and the first boats might be ready by the summer of 1944.

  After Hitler approved this scheme, Dönitz ordered about seven hundred such submarines: 450 1,600-ton oceangoing types (based on plans for the Walter Type XVIII “Atlantic boats,” U-796 and U-797), which were designated XXI, and about 250 250-ton coastal types (based on the Walter Type XVIIA and B “Coastal boats”), which were designated Type XXIII. Owing to their massive battery power, the Germans called these two new submarine types “electro boats” to distinguish them from the conventional “diesel boats” or the hydrogen-peroxide “Walter boats.”

  Notwithstanding all the problems, work on the Walter hydrogen-peroxide boats continued to the end of the war. Apart from the test beds V-80 and V-300 (U-791), seven Walter boats were commissioned in the war, all ducks of 300 tons or less that had a load of four torpedoes (two in bow tubes and two reloads) and a submerged range of about 100-150 miles.*

  Numerous historians and engineers have extolled this achievement and some have speculated that had they been perfected and built earlier, the hydrogen-peroxide U-boats could have had a decisive impact on the war. This is nonsense. The hydrogen-peroxide boats were impossibly complex and dangerous and, in any case, Germany was in no position to provide the exotic fuel. For these and other reasons, in the postwar years the United States, Great Britain, and other nations declined to pursue this line of submarine technology.

  However, if they lived up to expectations, the “electro boats” were well positioned to provide the “new generation” of U-boats required to decisively outfight convoy air and surface escorts. But they were not to be ready in sufficient numbers for a year or more. In the interim, a radical upgrade was required to enhance the survivability of the VIIs and IXs.

  Professor Walter provided that upgrade as well: the Schnorchel, or in the English spelling, snorkel, known among all submariners colloquially as the “snort.” This was a double-barrel tube that could be raised above the water or lowered beneath it like a periscope while the boat was running submerged. One barrel of the tube sucked in air to run the diesel engines submerged; the other barrel expelled the diesel exhaust. Conceived primarily as a defense against enemy radar-equipped aircraft, the snort allowed U-boats to charge batteries submerged with the diesels at a speed of up to 5 or 6 knots, offering only a very small radar target.

  The snort was not a new idea. In the previous fifty years, numerous submarine designers had incorporated snorts in their proposals. The Dutch had built several submarines in the 1930s with snorts, some of which were captured by the Germans. However, it was believed that snorts could only be used effectively in relatively calm seas, never in the rough North Atlantic where the snorts would be continuously “dunked” by the big waves. When that occurred, the diesels would suck an enormous quantity of air from inside the boat, perhaps even from the lungs of the crewmen, and/or the carbon-monoxide exhaust would back up inside the hull and kill the crew. Besides those horrifying possibilities, snorting boats running submerged on diesels made a tremendous racket, easily detected by enemy hydrophones and other passive sonar devices, while at the same time “deafening” the submarine. A submerged snorting boat thrusting its full girth against resisting seas also would use almost twice the fuel oil of a surfaced U-boat.

  Incorporating some features of the Dutch model, Walter’s snort was of advanced engineering design, which eliminated many of the weaknesses and drawbacks of earlier versions. Both ends of the tube had sensitive valves and floats to prevent spray inhalation or flooding and exhaust backup. Walter demonstrated that even if the air intake “dunked” and closed for a full minute, the air sucked from inside the boat would not be physically harmful to the crew, merely annoying. Accordingly, in June 1943, Dönitz and the OKM directed that the school ducks U-57 (Erich Topp’s old command, which had been rammed, sunk, and salvaged) and U-58, and the VIICs U-235 and U-236, which had been sunk during an Allied air raid on Kiel on May 14 and salvaged, be fitted with snorts for test purposes.

  The tests were far from satisfactory. Mounted on the port side just forward of the bridge, the exhaust or wake of the snorts on the two VIIs clouded the raised periscopes, reducing submerged visibility. When the snort dunked, the suction inside the boat was much greater and more rapid than predicted. Hence it became necessary when snorting for one engineer to maintain a continuous close watch on a barometer. When the pressure inside the boat suddenly dropped below a normal 1020 millibars to 850 millibars, he shut down one diesel. If the pressure fell another 100 millibars to 750, he shut down the other diesel and shifted to battery power. Notwithstanding all efforts to prevent it, diesel fumes seeped into the boat, causing crewmen headaches and blurred vision or more serious illnesses.

  Hailed by some historians and engineers as another great technical achievement, the snort was not that by a long shot. Rather it was a miserable, temporary device that German U-boat crews hated absolutely. They resisted its installation on their boats and used it not continuously, as often depicted, but only very sparingly (ordinarily about four hours a day) to charge batteries, owing to the high fuel-oil consumption experienced when running submerged on diesels. In his memoir, Iron Coffins, Herbert Werner described what happened when the ball float in the snort air intake jammed shut, creating a vacuum in the boat:

  The men gasped for air, their eyes bulging. The Chief [engineer] lowered the boat, bringing the Schnorchel head below surface in an effort to loosen the float. To no avail. Breathing became ever more difficult; suffocation seemed imminent. The Chief gesticulated wildly, trying to tell his men to lay down the air mast, which might result in unlocking the float. With agonizing effort, the mechanics turned handles, lowered the mast by cable, then erected it again with the primitive winch.* Painful minutes passed, but then the mast drained and the seawater gurgled down into the bilges. The float cleared with a snap and air was sucked into the boat with a long sigh. The sudden change in pressure burst many an eardrum. Some of the men covered their faces in pain and sagged to the deck plates. Others swallowed violently to equalize the pressure.

  Owing to crew complaints and technical bottlenecks, the Germans fitted the snort much more slowly than usually described. The OKM ordered the first twenty snorts for operational boats in August 1943, and another 140 in late September. First priority went to boats already at the battlefronts and secondly to new construction. The “electro boats” were also to have snorts.

  Pending the arrival of “electro boats” and “snort boats,” Dönitz proposed to continue the U-boat war on a reduced scale with upgraded Type VIIs and IXs, employing some changes in tactics. The upgrading and new tactics were as follow:

  • A new FuMB, or radar detector, called Wanze, built by the German company Hagenuk, to replace Metox. Still doubtful that the Allies had adapted an airborne centimetric-wavelength ASW radar and convinced that the Allies were “homing” on the electronic emanations from Metox, the Germans put the supposedly nonradiating Wanze, whic
h searched in the eighty-centimeter range, into production. But, of course, it was useless against the centimeter-wavelength ASV radar that had become standard issue in Coastal Command and the American ASW commands. Until Wanze arrived, U-boat Control directed that U-boats were only to operate on the surface with one electric motor at night or in foggy weather so the bridge watch could “hear” enemy aircraft approaching.

  • The new T-5 Zaunkönig (Wren) antiescort acoustic or homing torpedo, a “wonder weapon” to replace the less than satisfactory T-3 Falke, Capable of homing on ships traveling at speeds of up to 15 knots, the faster Zaunkönig, it was believed, would at the very least put U-boats on an even footing with most escorts.

  • Increased numbers of G7a FAT I (looping) torpedoes made possible by the conversion of G7as formerly carried in topside canisters, which had been abolished. The FAT I was to be fired only at night and was fitted with only an impact pistol (AZ).

  • The new FAT II, a G7e electric torpedo that could be fired submerged. It was designed not only to loop but also to circle. It was to be used against escorts until the Zaunkönig was debugged and fully operational.*

  • An improved version of the Pi2 pistol for G7e (electric) torpedoes that could be set for either impact (AZ) or magnetic (MZ) detonation.

  • Increased numbers of flak guns, notably a new quad 20mm (aft of the bridge on a bandstand) to allow U-boats to better counter Allied air attacks. The interim goal was to modify and equip the bridges of all Atlantic force U-boats with a quad 20mm gun, two single or twin barrel 20mm guns, and four dismountable .50-caliber machine guns. The fact that the bulky quad 20mm, which had splinter shields, somewhat destabilized and slowed the boats while diving and running submerged had to be accepted.