Decoding History: The Battle of the Atlantic and Ultra. Annapolis, Md.: Naval Institute Press. . - book review

Naval War College Review, Summer, 2001 by Christopher Bell

Gardner, W. J. R. Decoding History: The Battle of the Atlantic and Ultra. Annapolis, Md.: Naval Institute Press, 1999. 263pp. $34.95

For thirty years after the Second World War, historians said very little about the role of signals intelligence in the Battle of the Atlantic--because either they did not know about the Allies' remarkable code-breaking successes, or they could not write about what they did know. That changed in 1974, when revelations about ULTRA exposed the full extent of the Allied penetration of Germany's signals. Unfortunately, in the subsequent rush to rewrite the history books to include ULTRA, its significance was frequently inflated.

In this study of ULTRA and the Battle of the Atlantic, Gardner offers the most fully developed case yet that monocausal explanations for the Allied victory in this campaign are inadequate--that ULTRA was only one critical factor among many. Gardner provides two case studies to support his argument. The first demonstrates that Britain's growing ascendancy over the U-boat in 1941 had many causes, most of which were unconnected with ULTRA. Just as important as code breaking, if not more so, was the tightening up of the convoy system and the German decision to shift U-boat operations westward in order to avoid the increasingly hostile environment around the British Isles. The greater availability of escort vessels and growing American assistance also played an important part in turning the tide in Britain's favor in 1941. It is therefore a mistake to suggest, as some have done, that ULTRA alone may have saved as much as two million tons of shipping during this period.

Gardner's second case study covers the period from mid-1942 to mid-1943, the final turning point in the campaign. Once again, he makes a strong argument that factors other than ULTRA were essential for the Allies' success, most importantly the closing of the mid-Atlantic "air gap" and the increasing number and effectiveness of Allied escort vessels. By 1943, Gardner notes, it was more hazardous than ever for the Germans to attack convoys. At the same time, the growing number of U-boats operating in the mid-Atlantic made the evasive routing of convoys extremely difficult for the Allies, even when ULTRA was available on a timely basis.

These case studies cover periods when ULTRA was most valuable because Germany was employing its U-boats in "wolf pack" attacks on convoys. When U-boats operated individually rather than in groups, which was the case for nearly two-thirds of the war, ULTRA's value was much less. Gardner also emphasizes that there were lengthy periods when German signals were being read only after considerable delay. For much of the war, he concludes, ULTRA'S principal use was to enable the Allies to build up a general picture of the size and methods of the German U-boat fleet. It seldom had any impact on the Battle of the Atlantic at the operational or tactical levels.

This book deliberately focuses on the turning points of the campaign and the broad relationship of ULTRA to other factors; it does not provide either a blow-by-blow account of the Battle of the Atlantic or a systematic examination of ULTRA's employment by Allied commanders. The period from June 1943 until the end of the war is largely ignored. However, Gardner devotes a considerable portion of this book to background information about the Battle of the Atlantic, including the importance of economic factors, the role of technology, Germany's own code-breaking activities, and the workings of convoy. This material should be useful for the general reader even if it offers little for the specialist.

Gardner's broad conclusions are carefully reasoned and well balanced. The Battle of the Atlantic would have been a harder and costlier struggle without ULTRA, but the Allied victory cannot be solely attributed to code-breaking successes. Decoding History will not be the final word on signals intelligence and the Battle of the Atlantic, but it may put an end to the wildly exaggerated claims that are sometimes made for ULTRA.