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

by Clay Blair

  In follow-up operations against the Allied forces engaged in the invasion of Italy, five boats achieved successes in October.

  • Waldemar Mehl in the U-371 sank three confirmed vessels: the 7,200-ton American Liberty ship James R. Lowell; the 700-ton British minecraft Hythe and—most notably—the new (1941) American fleet destroyer Bristol, which was escorting a convoy near the Algerian coast and went down in ten minutes. The American destroyers Trippe and Wainwright rescued fifty-two men from Bristol, but 241 others perished, a terrible American tragedy.

  • No less significantly, off Naples, Siegfried Koitschka in U-616 sank the new (1940) American destroyer Buck, which two months earlier had sunk the Italian submarine Argento. The American destroyer Gleaves and a British LCT rescued ninety-seven crew, but about 150 others perished, yet another American tragedy.

  • Victor-Wilhelm Nonn, age twenty-six, new skipper of U-596, sank a 5,500-ton Norwegian tanker near Tobruk.

  • Karl-Jürgen Wächter in the newly arrived U-223 sank a 5,000-ton British freighter off the coast of Algeria.

  • Dietrich Schöneboom, age twenty-five, in U-431, claimed sinking three freighters for 26,000 tons, the probable sinking of another freighter of 10,000 tons, and damage to yet another of 12,000 tons. Although none of these claimed hits could be confirmed, Schoneboom won a Ritterkreuz for these and other alleged successes.†

  During these operations, another U-boat was lost inside the Mediterranean.

  On the night of September 10, a Leigh Light-equipped Wellington of British Squadron 179, piloted by a Canadian, D. B. Hodgkinson, found the highly decorated Albrecht Brandi in U-617 about one hundred miles east of Gibraltar near the coast of Spanish Morocco. Attacking into “heavy” flak, Hodgkinson dropped six depth charges that disabled U-617. Three hours later, in the early hours of September 11, another Wellington from that squadron, piloted by W. H. Brunini, arrived and, in the face of “intense” flak, dropped six more depth charges.

  These attacks so badly damaged U-617 that Brandi could not dive. To avoid certain capture, he drove the boat into shallow water offshore and abandoned ship. After he and the crew reached the beach, Spanish troops took the Germans into custody. However, they were soon released and returned, via Spain, to Toulon, where Brandi, who had added to his laurels with this “escape,” was given command of another boat, U-380.

  After dawn on September 11, swarms of Hudsons and Swordfish of British Squadrons 48, 233, 833, and 886 (based at Gibraltar) located the abandoned hulk of U-617 and attacked with bombs and rockets. Three warships (British corvette Hyacinth, British trawler Haarlem, Australian minesweeper Woollongong) then arrived to shell U-617 into smithereens. Pilot Hodgkinson, the Canadian who originally found and disabled U-617, won a DFC.

  “CAIN,” “ABEL,” AND OTHER SIBLINGS

  At the National Cash Register Company in Dayton, Ohio, the Naval Computing Machine Laboratory (NCML) completed two more Model 530 four-rotor prototype bombes, “Cain” and “Abel.” These embodied improvements suggested by the first two prototypes, “Adam” and “Eve.” The first “formal” (or production) Model 530 was delivered on July 4 and had its first test run at the lab on July 23. According to the historian Colin Burke, by the end of July 1943, fifteen Model 530s had been completed, “but none would work!”

  As Burke recounted the story, the main technical defect lay in the “Bakelite code wheels.” As before, when run at the required extremely high speeds, the wheels distorted and failed to make proper electrical contacts. By July 26, Burke wrote, the chief electrical engineer at NCR, Joe Desch, as well as the Navy lab chief, Ralph Meader, and others “feared the American bombe might never be made operational.” These men, Burke wrote, “almost declared” that a year of frenetic work had been wasted and “the American bombe came near to being abandoned.’’

  Whether or not this Burke version of events is fair, accurate, and sufficiently complete cannot be judged until the National Security Agency releases the “RAM File” documents to which the agency gave Burke exclusive access for his book. As related, in his understandable eagerness to credit the genius of Joe Desch, Burke apparently found it necessary to depict Desch and Howard Engstrom as technical antagonists, usually resulting in victory for Desch and defeat for Engstrom.

  Whatever the truth of the matter, Burke wrote that it was Joe Desch who saved the day. “Desch predicted that careful storage, handling, and refurbishing would solve the problem.” “Again his judgment was trusted,” Burke continued. “The wheels were reworked and production was resumed based on his hope that last-minute modifications would provide a permanent cure.” Apparently his solution worked. “Desch’s bombes proved to be very, very reliable,” Burke concluded. “After their first shakedown runs, they could be used twenty-four hours a day.”

  According to the previously described Engstrom “Bombe History,” NCR turned out about four bombes per week over the summer of 1943. In early August, OP20G directed Dayton to prepare to ship bombes to Washington as soon as the new two-story building at the Nebraska Avenue facility was ready to receive them. Dayton shipped four bombes on September 1 in heavily guarded railway cars. Seventy-three men and women from Dayton reported to Nebraska Avenue to run and repair these machines: thirteen officers (three Waves) and sixty enlisted persons (fifteen Waves). This unit, which expanded quickly to hundreds, was designated OP20G4E.

  By the end of September 1943, there were seventeen Model 530 bombes in operation at Nebraska Avenue. Eleven other machines had arrived but were “not set up.” However, by October 15, thirty-nine bombes were running and by November 1, forty-four. By January 1944, eighty-four bombes were on line.

  Concluding his history, Engstrom wrote generously in April 1944:

  From a position of subordination in the [U-boat Enigma] problem, we have, by superior performance, gradually assumed a dominating position in the submarine problem. The part played by the British in the success of our work should not, however, be minimized. While it is possible that we might have been able to proceed independently, they have supplied elements, such as wheel wirings, absolutely essential to an early solution of the problem.

  Their coverage of the entire Enigma field and their resulting strong position with regard to cross-cribbing, as well as their ability to obtain physical possession of German cryptographic equipment and documents, make it highly advisable that we endeavor to maintain our present relations in this problem, despite their failure to carry out their obligations along certain lines.

  The Americans concerned pledged never to reveal the secrets of breaking Enigma. The Britons concerned likewise pledged, but beginning in 1974* they began to leak the secret at such a fast rate that both London and Washington were finally compelled to declassify and release official documents. In the Niagara of British books about breaking Enigma, however, the fact that the British were unable to cope with four-rotor Triton and that from the fall of 1943 onward the Americans took over the job is almost never mentioned. If it is, the reference is so slight as to have no impact whatsoever.

  Another reason historians and writers have ignored the American contribution to breaking U-boat Enigma is the belief that by the summer of 1943, the U-boat force was utterly defeated and therefore the information from the American decrypts was of little value. This, of course, is wildly untrue. As related, in March 1943, the Allies had projected a huge net increase of the U-boat force to 613 boats by year’s end. In addition, they were aware from Enigma decrypts of the upgrades planned or in progress on the old boats (snorkels, microwave radar detectors, more powerful flak arrays, T-5 homing torpedoes, and so on) and the ongoing German crash program to build the high sprint-speed Type XXI and Type XXIII “electroboats” and the even faster hydrogen-peroxide Walter U-boats. Therefore, every scrap of information on German U-boats then and to the end of the war was of vital importance to those charged with countering the menace they posed.

  The Allies also faced daily the possibility that the Germans might increase the compl
exity of naval Enigma or even adopt an altogether new cryptographic system. Therefore the R&D work of Howard Engstrom’s OP20G section continued at a relentless pace to the end of the war. He and his men produced a substantial number of exotic new devices that kept the Allies one step ahead of the Germans. Other projects proved to be important contributions to the birth of the computer age.

  On the other side of the Atlantic, German codebreakers at B-dienst faced grave difficulties. When on June 10 the Allies began the shift from the compromised Naval Cypher Number 3 to Naval Cypher Number 5, the Germans lost the great flow of specific information on Allied convoy cycles.

  B-dienst, however, was able to keep track of the convoy cycles on the North Atlantic run by other means. These included sporadic breaks in a low-level British naval code and the Allied merchant-ship code, describing “straggler routes”* and by traffic analysis and, occasionally, radio-direction finding. In early September, B-dienst proudly reported to the OKM that of the forty-nine loaded convoys on the North Atlantic run eastbound from the Americas to the British Isles that sailed between May 25 and September 3, it had obtained information from “radio sources” on all but five.

  This information, plus past experience and intuition, enabled B-dienst to figure out convoy cycles on the North Atlantic run through much of September and October 1943. The Germans concerned knew that the information derived from “a secondary cypher” (as Dönitz put it), and they were aware that this source was likely to dry up at any hour. However, B-dienst codebreakers assured Dönitz and Godt that by mid-October the Germans would crack Naval Cypher Number 5, thus restoring German codebreaking supremacy and again providing U-boats with precise convoy information. As will be seen, this did not come to pass; the Germans never broke Naval Cypher Number 5.

  Meanwhile, yet another report that the Allies were reading naval Enigma arrived in Berlin. This one came from the Kriegsrnarine organization in Switzerland. The report stated quite accurately: “For some months German Naval codes giving orders to operational U-boats have been successfully broken. All orders are read currently.” The report named the source as a “Swiss American in an important secretarial position in the U.S. Navy Department.” †

  This report initiated yet another urgent reexamination of Enigma security. The chief of naval communications, Erhard Maertens, oversaw the investigation personally. Inasmuch as there had been no North Atlantic convoy battles since the U-boat withdrawal on May 24, his men focused on U-boat refueling rendezvous. They found that between June 6 and August 1, there had been twenty-one such meetings and that eight (or about one-third) had been “disturbed” by enemy aircraft. Maertens glibly dismissed these “interruptions” as lucky finds by land-based reconnaissance aircraft and/or carrier-based aircraft passing close by.

  One reason at this time for the very high confidence in Enigma security was the incorporation of a top-secret procedure believed to thwart any possibility of an enemy cracking the code. This was a Stichwort permutation that completely altered the Enigma inner and outer key settings. A permutation of keys by the Stichwort procedure had taken place nearly every fortnight, on June 20, July 6, and July 23.*

  Details of the Stichwort procedure were very closely held in German inner circles. A German document explained:

  At U-boat Control’s radio station, the changing of the Stichwort is always undertaken by one and the same officer. Apart from him no one knows the key to the Stichwort procedure. The Stichwort, followed by a number, is transmitted [to the U-boats] by signal. On board [the U-boat] also the permutation may only be made by an officer. The key to the Stichwort procedures is never kept in writing on board [the U-boats] but the officer whose business it is makes an inconspicuous note of it and has to keep the details of the procedure in his head. On board [the U-boats] the radio room is given [only] the results of the Stichwort calculation and sets up [the Enigma] machine accordingly. The use of a Stichwort excludes the possibility of the enemy reading our traffic by cryptographic means.

  Further investigation by the communications department revealed that between August 3 and August 8, when the July 23 Stichwort procedure was still in effect, U-boat Control arranged ten more refueling rendezvous. Allied aircraft interrupted nine of these meetings and Allied surface ships the tenth. That, Maertens said, certainly indicated foreknowledge on the part of the Allies for this Stichwort period, perhaps an Enigma capture. Against that, however, was the fact that several home-bound U-boats utilized the route close along the north coast of Spain and were not molested. In any case, the Stichwort was changed on August 11, the day after the report from Switzerland. Moreover, Maertens reported, henceforth the Stichwort would be changed weekly, beginning on August 16, and a “different method” would be employed.

  In conclusion, Maertens wrote,

  The Chief of Naval Communications Department holds to the opinion he expressed in the spring of this year when there had been grounds for suspecting compromise or betrayal of keys. That is: The Chief of Naval Communications Department considers that continuous current reading of our radio traffic by the enemy is out of the question.*

  RETURN TO THE NORTH ATLANTIC: GROUP LEUTHEN

  In September 1943, the beginning of the fifth year of the war, the Atlantic U-boat force was hard-pressed to carry on. The ASW campaign in the Bay of Biscay during the summer by RAF Coastal Command and supporting naval forces had inflicted horrendous losses on the attack boats and U-tankers alike. Hitler had further reduced the strength of the Atlantic force by his orders to divert eight new Type VIIs to the Arctic in July and August, and to transfer seven Type VIIs from the Atlantic to the Mediterranean. In addition, eight Type VIIs of the Atlantic force had been converted to flak boats. The usual modifications, accidents, and losses in the Baltic † had delayed the arrival of other attack boats.

  Taking into account new arrivals and loses, and transfers to and from the Arctic and to the Mediterranean, in the fall of 1943 the strength of the Atlantic force remained modest and virtually static.

  Reflecting the decision of Admiral Dönitz to reopen the U-boat campaign on the North Atlantic run that fall, U-boat Control sent the great majority of the available boats to that area.

  The U-boats deployed in the North Atlantic were to confront ever-increasing numbers of radar-equipped land-based and carrier aircraft, as well as experienced escort and support groups composed of destroyers, sloops, frigates, and corvettes.

  Owing to the U-boat stand-down in August, the weariness of Allied aircrews, and aircraft maintenance requirements, the ASW air offensive in the Bay of Biscay mounted by John Slessor’s Coastal Command diminished in intensity. From about September 1, the newly arrived U.S. Navy Fleet Air Wing 7* began to assume greater and greater responsibility for air patrols over the Bay of Biscay. By October, according to its historian, the wing flew about half of all daylight missions mounted by the Allies.

  This fairly powerful but seldom mentioned U.S. Navy land-based air unit performed yeoman ASW service over the Bay of Biscay in the fall of 1943. In September, the wing flew 1,888 hours of ASW patrols; in October, 2,109 hours; and in November, 2,521 hours. In that period the wing lost nine B-24s in combat † or in accidents or to unknown causes. On these long, arduous Biscay patrols the Americans rarely spotted a U-boat and probably attacked only two or three, splitting credit for one kill with RAF aircraft.

  The diminished intensity of the land-based air offensive in Biscay was offset in part by the Allied naval airpower based at sea. It emerged that fall as a significant ASW force. Twenty-three American-built “jeep” carriers had been commissioned in the Royal Navy. Of the original five Archer-class, Avenger had been sunk by a U-boat; Dasher had blown up in the Firth of Clyde; and Archer, plagued by chronic engine failure, had been withdrawn from combat to serve as a barracks and stores ship. That left Biter and the much-delayed Tracker of that group for escort duty on the North Atlantic convoy run. Of the larger Bogue-class, ten had arrived in the British Isles. After modifications, Battler went to
the Indian Ocean; Attacker, Stalker, and Hunter went to the KM and MK convoy routes; and Fencer was placed on standby for the British occupation of the Azores (Operation Alacrity). Five other Bogue-class carriers, commissioned in April or June 1943,* were in British yards for modification. Eight Long Island class (British “Ruler “-class) were still in workup in American waters, †

  As related, U-boat Control formed group Leuthen, composed of twenty-one upgraded Type VII boats, to reopen the campaign in the North Atlantic. From August 23 to September 9, eighteen experienced boats sailed from France and three new boats from layovers in Norway. The group was to be supported by one of the two remaining Type XIV “Milk Cow” U-tankers, U-460, commanded by Ebe Schnoor.

  To cope with Allied aircraft, which had thwarted the assembling and attacks by U-boat groups on convoys in prior engagements, the Leuthen boats were to employ a revised tactical doctrine. Like the boats crossing the Bay of Biscay in June and July, the Leuthen boats were to remain on the surface and fight back when detected by enemy aircraft. The new Wanze radar detector, which searched only in the meter-wavelength band and supposedly did not give off detectable emissions (as did Metox), would alert the U-boats to the approach of enemy aircraft in time to fully man flak arrays. The newly installed quad and twin 20mm flak guns were supposed to give the U-boats sufficient firepower to repel even the most formidable aircraft, including B-17s, B-24s, and Halifaxes. When challenged by an enemy aircraft, a U-boat was to broadcast to Control and to other U-boats a special short-signal (“A/A defense”) so that whenever possible the other U-boats could come up and add the support of more flak guns.