Chapter V
The Shift to the Middle and South Atlantic

  1. Withdrawal from the North Atlantic.
    1. Review of causes of the German loss of initiative.
    2. The German date: 23 May 1943.
    3. The present superiority of enemy radar . . .

  2. Attempt to continue group tactics in the Middle Atlantic. 24 May - July 1943.
    1. Influence of German radio intelligence.
    2. Considerations of Allied defense.
    3. Allied radio intelligence.
    4. Failure of Trutz.

  3. Dispersal of U-boats to distant areas.

  4. Vulnerable points:areas of transit and refueling rendezvous.
    1. The Biscay offensive.
    2. The refueling stations, their necessity and destruction.



  1. Withdrawal from the North Atlantic.

    By the end of May 1943, convoy warfare in the North Atlantic had been abandoned by German U-boat Command, not to be renewed - and then on a much reduced scale - until September. The power of the wolf pack had been broken. Not only had the tonnage sunk declined markedly from March to April and again from April to May, but the rate of U-boat killings for the month of May had shown a startling and decisive increase. 42 were destroyed in the Atlantic area during May, as against 13 in April and 15 in March. The fruits of convoy warfare were no longer worth the investment.

    1. Review of causes of the German loss of initiative.

      In this victory over the wolfpack, innumerable causes, including at certain decisive moments, weather and doubtless plain luck, had played their part. But the manifest prime reason is the growing superiority of the Allies in equipment and technique, and here the increased number and range of anti-submarine aircraft, the out-stripping of the Germans in radar, and the success of British-American radio intelligence may be set down as perhaps the leading factors. German U-boat Command, in his attempt to find alternative uses for his U-boats after abandoning North Atlantic convoy operations, would continue to be harassed by his inability to compensate for Allied superiority in these respects. From now on the conduct of the U-boat war, once so boldly offensive, takes on increasingly the character of makeshift and evasion, the search for countermeasures and counter tactics. The initiative in the Battle of the Atlantic had passed to the Allies.

    2. The German date: 23 May 1943.

      As has been seen in the preceding section, several points in the period March - May 1943 might be singled out to punctuate the gradual defeat of the wolfpack. The sharp decrease in convoy tonnage sunk during the last 10 days of March as compared with the extremely heavy losses of 1-20 March, marks one turning point. Perhaps the successful defense on 5-6 May of convoy ONS 5 against the large


      disposition (about 40 units in all) of U-boats that attacked it, with at first considerable prospect of doing serious damage, marks another. But the process of driving the packs out of the North Atlantic was after all a continuous and cumulative one. No single moment can be taken as absolutely decisive. By 23 May, however, the point of terminus at least is definite. By 23 May, V-boat Command had made his decision to fish in less troubled waters.

    1. The present superiority of enemy radar.

      U-boat Command's important general message (Offizier 1753/23 May) addressed "To All U-boat Commanders," has been quoted in full at the end of Chapter IV. There, it has been seen, Dönitz surveys the unfavorable U-boat situation, traces it primarily to "the present superiority of enemy radar instruments and the surprise from the air thus made possible," asserts that his whole energy is engaged in the improvement of German radar, search receiving and anti-aircraft defense, and meanwhile promises suitable changes in the choice of attack areas. The latter promise was put promptly into effect. In Offizier 1106/24 May, 16 U-boats - comprising the majority of the survivors of the month's convoy operations - were ordered to proceed to positions within a radius of 30 miles of 35° 15'N 42°05'W. This, as later developments made clear, was the sign of the decisive shift in strategy that was demanded by the failure of the May campaign. By the beginning of June large scale operations on the US-England convoy routes had been suspended, and the attempt to transfer group tactics to the Middle Atlantic - the first of a series of expedients to keep the U-boat in some degree effective - had begun.

  1. Attempt to continue group tactics in the Middle Atlantic. 24 May - July 1943.

    1. Influence of German radio intelligence.

      17 U-boats, including most of those addressed in 1106/24 May, were ordered in 1656/26 to form Group Trutz, and to place themselves by 0800/1 June in a patrol line extending from 38°45'N - 43°26'W to 32°03'N - 43°26'W. This, German U-boat Command's first attempt since March to cut the US-Gibraltar convoy route by group formation, had both an


      immediate and a more general motive. There is evidence that not only the exact time and position ordered for the patrol line, but the original order (1106/24) to head for the area, were the result of German knowledge by cipher compromise of the route of Flight 10 and possibly also of GUS 7A.1 In 1832/27 May the expected passage of a west-east convoy, presumably to be identified as Flight 10, is announced to Group Trutz; in 1021/1 June the group is instructed to be ready from noon of that date for a westbound convoy also - presumably GUS 7A.

    1. Considerations of Allied defense.

      But while the exact timing and location of Group Trutz's patrol line were undoubtedly determined by Command's radio intelligence, the basic fact of the shift itself grows out of the strategic situation in the Atlantic, outlined above. A U-boat group operating in the Middle Atlantic would be beyond the range of shore based aircraft, hitherto the U-boats greatest enemy. True, the operation against SC 129 and HX 237 in the middle of May had demonstrated that those convoys which were beyond land-based coverage in the North Atlantic could now be effectively protected by auxiliary carriers.2 Command may have well supposed, however, that the surprise move of drawing up a patrol line across the US-Gibraltar route in the Middle Atlantic would find the anticipated convoys (as all previous convoys on this lane had been) without escort aircraft carrier (CVE) protection. It is notable that Current Order Number 11 ("Atlantic Defense Situation," later Current Order Number 21), included a warning against surprise by carrier aircraft in the Middle as well as the North Atlantic, was not promulgated until August 1943. Command's apparent failure to foresee the extension of Allied air power - primarily in the form of CvE task groups - is in fact one of the essential weaknesses of his conduct of the U-boat war from May through July of 1943. This failure is particularly evident in the


      neutralizing of Group Trutz by carrier aircraft and in immediately subsequent U-boat disasters in the Middle Atlantic brought on by carrier air power.

    1. Allied radio intelligence.

      In the direction of this power against Group Trutz - itself drawn up on the basis of German radio intelligence - Allied radio intelligence played an initially decisive role. Though 1656/26, the message actually forming the group, was not read until 7 June, the general position, and the number of U-boats ordered to head for it, were known from 1106/24 May, which had been read currently. In consequence Carrier Task Group (CTG) 21.12 was ordered to operate against submarine concentrations in the area of 35°N - 45°W in support of convoys UGS 9, GUS 7A and Plight 10. GUS 7A was diverted south of the Trutz line; on the evening of 4 June, Flight 10 was approaching the line at the point where, according to 1832/9 May, the Germans were expecting it. Before Trutz could make contact, aircraft from the USS Bogue had found the southern end of the line and bombed it. Three U-boats were attacked in rapid succession, two with promising results. A gap in the German traffic read, (1-4 June) makes it impossible to say exactly what was the effect of these attacks from the U-boats point of view. One U-boat, Reichenbach (U-217), was evidently sunk; others must have been forced to take avoiding action or to remain submerged for extended periods, for there is no evidence that Trutz ever made contact,3 much less fired a shot, on Flight 10.

    2. Failure of Trutz.

      At 2306/5 the Trutz patrol line was canceled and the submarines ordered to head north for refueling rendezvous in 37°03'N - 40°54'N and 37°57'N - 44°30'W. This signified the abandonment of the convoy operation originally planned.


      Despite U-boat Command's prompt action on excellent intelligence, his attempt to shift group tactics to the Middle Atlantic started with failure. This failure was to continue during Group Trutz's existence through June and early July. During this time Group Trutz was re-formed and its position several times shifted, but there is no record in traffic read of its fighting a single convoy operation, or, in fact, making a single contact with Allied shipping. After the failure of Group Trutz, the attempt to carry on convoy warfare was abandoned for the rest of the summer. No further group was formed in any area of the Atlantic until September.

  1. Dispersal of U-boats to distant areas.

    Meanwhile U-boat Command was developing other expedient to compensate for his withdrawal of wolfpacks from the North Atlantic. Individual U-boats coming out of Norway into the North Atlantic were on several occasions ordered to simulate group activity with dummy radio traffic.4 The majority of U-boats sailing from Biscay bases, however, were ordered to distant waters - the Caribbean area and the coasts of Florida, Brazil and various points along western Africa being the favorite headings. Distant cruises by independent U-boats were of course a familiar element in Command's overall strategy; but in the summer of 1943, for the first time, they absorb the major strength of the U-boat arm. A policy of dispersal has been substituted for one of concentrated attack. Command must have regarded the policy, even on the extensive scale on which it was executed in the summer of 1943, as a diversion rather than a main blow. It was a method of harassing enemy shipping and tying down enemy defenses in remote coastal areas, pending the production of the equipment which would permit the renewal of convoy warfare in the North Atlantic.

  2. Vulnerable points: areas of transit and refueling rendezvous.

    This dispersive strategy avoided the risk of collective destruction such as had been visited upon certain North


    Atlantic groups in May. There remained, however, two points at which individual U-boats were brought together within a limited area, and so presented a concentration of targets which invited attack. The first was the area of transit to and from port, particularly the Bay of Biscay. The second was the refueling rendezvous on which most cruises to distant areas were dependent. These vulnerable points offered the openings through which Allies drove home their successful antisubmarine offensive in the summer and fall of 1943.

    1. The Biscay offensive.

      In June 1943 the British inaugurated what they called the Biscay Offensive. The cessation of convoy warfare in the North Atlantic had liberated considerable forces which had been absorbed in escort duties during the winter and spring. An increased number of aircraft and surface units could thus be assigned to the patrol of the restricted area through which the great majority of Atlantic U-boats had pass both in cruising out to sea and in approaching port. Intensive training in antisubmarine tactics was carried out, and new methods were developed. The Biscay Offensive was a notable success. U-boat kills in the Biscay area were consistently high throughout the summer months of 1943, reaching a peak of 18 in July, and accounting for a large proportion of the total number of U-boats sunk in all areas between May and September.

    2. The refueling stations, their necessity. and destruction.

      The Biscay Offensive was essentially a British enterprise, though U.S. aircraft participated. The attacks on refueling rendezvous in the Middle and South Atlantic during the summer and fall of 1943 were in the hands of the U.S. Navy, being chiefly the work of CVE task groups. These attacks, though less significant in actual numbers of kills than the Biscay Offensive at the latter's peak, had as one of their effects the reduction of German Command's all-important fleet of supply U-boats and, consequently, the continuous disruption of his refueling plans for the entire Middle and South Atlantic. Moreover, the attacks on supply rendezvous were in a number of instances directly determined by radio intelligence passed


      by OP-20-G. For these reasons the antisubmarine activity of carrier task groups, centering in attacks on refueling operations, will receive the chief emphasis in the present study.

      1. Necessity for U-boat refueling stations.

        Command's policy, during the summer of 1943, of dispersing his U-boats to distant areas required continuous and extensive refueling in the Middle Atlantic. This requirement was increased by the fact that there were not enough 750 ton U-boats available to meet the demands, and 500 tonners originally intended for operation in the relatively near waters of the North Atlantic - had to be used for most of the distant cruises ordered. Even the 750 ton IXc boats, with a cruising range at 10 knots of about 12,700 miles, required some refueling if they were to operate for an effective period in distant waters. The requirements of some 500 ton type VIIc, with a range at the same speed of about 8,400 miles, was correspondingly greater. Thus, owing to the necessity of frequent refueling rendezvous, the strategy of dispersal turned out to be subject to the very danger which it was designed to avoid - attack by aircraft on U-boat concentrations.

      2. Destruction of the U-tanker system.

        Here again Command failed to anticipate the extension and offensive application of carrier-borne air power. The first display of the latter's effectiveness against refueling operations followed closely on the frustration by carrier aircraft of Command's attempt to shift group tactics from the North to the Middle Atlantic. CTG 21.12, the very same task group that had broken up the southern end of Group Trutz on 5 June, moved on to do serious damage in an offensive sweep eastward of the Trutz position, culminating in the sinking on 12 June the sinking of the U-tanker, Czygan. This was the first of a mounting number of refueler sinkings which, as will be seen below, not only kept Command's plans throughout the summer in a constant state of uncertainty, but permanently wrecked the supply system on which his strategy was based.


Group Trutz - GUS 7A and Flight 10
29 May - 6 June 1943


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1. Flight 10 was a convoy of nineteen British LCI(L)'s bound for Africa.

2. Actually the Ranger and the Bogue and operated in the North Atlantic since March 1943; however, due to heavy weather, inexperience or pure luck, they appear to have made little impression on the U-boats.

3. There are several D/F's on unread transmissions from the Trutz area during the night of 4 June. It seems probable that these are reports of aircraft attacks rather than of contact with convoy. Had contact been made, there would almost surely have been some indication of the fact in the traffic from 1200B/5 June on, which was read. Furthermore, U-boats had been instructed in 1832/29 May not to report sightings of Flight 10 but to operate independently on what was offered.

4. Witzendorff and Schroeteler, 2212/9, 1547/23 June; Epp and Ehrich, 1143/17 June.

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