Brief Review of War in the Atlantic
Up to Reading of U-boat Traffic in December 1942
- Before US entrance.
The chart of monthly merchant shipping losses with comments which appears at the end of this chapter will suffice as a review of the major periods of the U-boat war from September 1939 to November 1941. In addition the following comments should be made:
- It was a primitive U-boat fleet which began the blockade of England on 3 September 1939, in a manner reminiscent of World War I. 250-tonners constituted the majority of a fleet that did not exceed 50 operational subs.
- Ocean going types were ready when it became advisable to move out into areas of weaker defense, but the U-boat operating fleet remained small.
- The introduction of the group attack ("wolfpack") against convoys was inevitable once off-shore areas were denied to individual U-boats.
- The marked improvement of the summer of 1941 was due to the combination of evasive routing and the use of Iceland as a base for escorts and aircraft. The "evasive routing" presumably represents the results of British decryption of U-boat traffic during this period.
- On the eve of US entrance into the war U-boat successes had been throttled down to the lowest monthly figure since May 1940, about 60,000 tons.
- A major cipher change cut off British special intelligence shortly after the United States entered the war.
- From US entrance to the beginning of Special Intelligence on U-boats. December 1941-December 1942.
When Germany declared war on the United States, a routine shift to the West brought the U-boat into the greenest pasture the war was ever to offer. With the assistance of
refueling stations at sea, U-boats pressed the war into harbors and river mouths of our own shores. It is not the purpose of this report to do more than remind the reader, if such reminder is necessary, that the rapid depletion of the Allied merchant fleet at the source of Allied supplies constituted the greatest single threat of defeat ever encountered in our war with Germany. Going on the high tide of Japanese conquests in the East and German conquests in Europe, Russia, and North Africa, 1942's appalling loss of shipping was a major factor in the tense gloom which awakened the US to the prospect of a long and costly struggle. It is in the province of this history, however, to point out that the German Navy was achieving this victory with an operational fleet still small when compared with the fleet that launched the North Atlantic offensive of the winter of 1942-43. The sinkings of June 1942 (626,158 tons) were achieved by the efforts of 60 to 65 U-boats in operation. The following winter the German Navy could put 180 U-boats into the Atlantic, 120 of which were operating while 60 were outbound or returning.
- Attack on US - Atlantic Seaboard. December 1941-Summer 1942.
Reaching a new high of success in March 1942 (approximately 535,000 tons), U-boats were temporarily checked in April by US countermeasures. The strengthening of our own defenses with the introduction of the coastal convoy system and the mobilization of every conceivable weapon, merely diverted U-boats once more into areas of weaker defense. With the extension of the U-boat campaign to the Caribbean and Gulf of Mexico our losses piled up to establish a new record for the U-boat fleet in early summer 1942.
- U-boats occupy more distant areas and at the same time return in force to the North Atlantic convoy lanes. From Summer 1942 - December 1942.
U-boats moved in greater numbers into the last outposts of the Atlantic. In addition to the Caribbean and Trinidad, always a point of emphasis, U-boats gathered along the South American coast, in the St. Paul Rocks area, along the African Coast, and finally in the Capetown and Madagascar areas. 1,200 ton U-cruisers were now ready to under take the most
distant missions. But only the larger boats could follow this natural movement into areas of weak defenses. The smaller U-boat (the 500 tonner) was built for North Atlantic operations and, as coastal areas within its reach were closed, it had to turn back to the mid-Atlantic. At the same time the renewal of interest in North Atlantic convoys had become a necessary condition for German victory. To offset the increased Allied convoy defenses in the North Atlantic, U-boats had to be massed in groups for quick and decisive kills of convoys which could be caught in the mid regions beyond land-based aircraft. This necessitated greater numbers of U-boats, a demand which the intense U-boat building program seemed adequate to meet. By November the German Navy could maintain an average of 90 U-boats operating in the Atlantic, and the Baltic was full of submarines in training.
- The critical nature of late fall, early winter 1942. Allied invasion of North Africa and the beginning of the all-out U-boat counter offensive.
The over-all critical nature of the period, November to December 1942 must be borne in mind. While the Russians held in the East, U.S. forces were just beginning the attempt to seize positions from which an offensive could be launched. There was no margin of safety. The U.S. effort in the Solomons, the landing in North Africa, the raising of the siege of Stalingrad, the battle of EI Alamein, all formed a picture of one force that had reached a limit and of an opposing force that was making its first impression. Whether the field was to be stabilized or whether the Axis force was to move forward once more depended on whether the enemy was permitted to rest, re-fit and to take advantage of his conquest.
The invasion of North Africa had taken the U-boat arm by surprise and forced an alteration of plans. U-boats had to be sent in large numbers to patrol the landing coast, the Gibraltar approaches, and the New York-Gibraltar lane in the mid-Atlantic. It was really the first occasion on which the hand of the German U-boat navy was forced. Hitherto it had, in a sense, merely followed the line of least resistance. And this policy had been justified in terms of the sheer numbers of ships sunk. The U-cruiser attacks off of Capetown, although definitely pointed toward assisting a specific German battle front, were still in conformance with this past development.
The invasion of North Africa served to emphasize the principle U-boat task, namely, the destruction of the convoys bound for England and Russia, by adding still another major convoy lane--still another artery of final defeat. The enlarged U-boat fleet was forced to undertake an intensive campaign against major convoys in the winter of 1942-1943. The importance of this campaign was clearly recognized by German High Command, and U-boat commanders were sternly reminded of their hard pressed comrades in Tunis and Russia. It was equally clear to the Allies that the one thing needed at this stage of the war was victory over the U-boat. Everything depended on maintaining our sea lanes. Could this be done, it was but a matter of time until the accumulation of materials would overwhelm the Axis. Hopeful as November may have been in view of the North African landing, Rommel's retreat, and Stalingrad, the U-boat had met the threat by its greatest single month of overall success.
Allied and Neutral Merchant Shipping Losses
November 1942 by U-boat Action
If the German armies seemed stalled on land, the U-boat was in a position to wipe out the momentary Allied relief. At this critical moment, the fundamental counter-offensive launched by the Germans may be said to have been the U-boat war at sea, for the sea itself was the basic Allied vantage point. It was into this situation that decryption intelligence entered in mid-December 1942. The decisive battle of the war had been joined at sea and there was no retreat for either side. Neither could refuse challenge in a bitter exchange of torpedoes and depth charges that followed.
Monthly Losses of Allied and Neutral Shipping by U-boat Action
Source: Admiralty. "The Anti-Submarine Report" CB 4050/Series. Figures represent thousands of GRT)
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