Report No. 51
of the
Operations Evaluation Group



This document contains information affecting the national defense of the United States within the meaning of the Espionage Act, 50 U.S.C., 31 and 32, as amended. Its transmission or the revelation of its contents in any manner to an unauthorized person is prohibited by law.

This volume is classified CONFIDENTIAL* in accordance with the security regulations of the War and Navy Departments.


* Declassified by Article 0414 of OpNav Instruction 5510.1B

Manuscript and illustrations for this volume were prepared for Publication by the Summary Reports Group of the Columbia University Division of War Research under contract OEMsr-1131 with the Office of Scientific Research and Development. This report was printed and bound by the Columbia University Press and was also issued as Volume 3 of Division 6 in the series of Summary Technical Reports of the National Defense Research Committee. It was originally published in duplicate form on 10 April, 1946, and was given wide distribution within the Navy Department.

Distribution of this volume has been made by the Chief of Naval Operations. Inquiries concerning the availability and distribution of this report and microfilmed and other reference material should be addressed to the office of the Chief of Naval Operations, Navy Department, Washington 25, D.C.



Charles M. Sternhell and Alan M. Thorndike


Operations Evaluation Group
Office of the Chief of Naval Operations
Navy Department


Washington, D.C., 1946


THIS volume embodies the results of some of the statistical and analytical work done during the period 1942-45 by members of the Anti-Submarine Warfare Operations Research Group of the U.S. Navy, later the Operations Research Group and, since September 1945, the Operations Evaluations Group. The group was formed and financed by the Office of Scientific Research and Development at the request of the Navy, and was assigned to the Headquarters of the Commander in Chief, U.S. Fleet. The group has been of assistance in:

  1. The evaluation of new equipment to meet military requirements.

  2. The evaluation of specific phases of operations from studies of action reports.

  3. The evaluation and analysis of tactical problems to measure the operational behavior of new material.

  4. The development of new tactical doctrine to meet specific requirements.

  5. The technical aspects of strategic planning.

  6. The liaison for the Fleets with the development and research laboratories, naval and extra-naval.

This book consists of a statistical review of the anti-submarine war in the Atlantic from 1941 to 1945, together with a unified analysis of the tactics which proved most useful in this combat. It is believed that this material will be of considerable help in providing basic understanding of this extremely important branch of naval warfare.

Certain aspects of the work of the group, which impinge on the antisubmarine problem, such as the Theory of Search and Screening and the more general Methods of Operations Research, will be embodied in other volumes to be published later.


Phillip M. Morse
Director, Operations Evaluation Group



THIS volume on antisubmarine warfare [ASW] represents a compromise between two major aims, to produce a unified summary of the events and problems of the antisubmarine war on the one hand, and to illustrate the scientific evaluation of naval operations on the other. The approach is fundamentally historical on both accounts, however, since the illustrations of scientific evaluation are taken from various analyses and studies made in connection with antisubmarine warfare during World War II. Great care should therefore be exercised in making predictions concerning the future of ASW from it. There is no guarantee that the antisubmarine measures successful in the past will continue to be adequate in the future.

A clear understanding of the events of World War II, their reasons and consequences, is necessary, however, as background for any decisions which are to be made in the postwar period. It is hoped that this volume may serve to some extent as a convenient reference and source of factual material. One overall conclusion is clearly evident from it: the introduction of new weapons, gear, and tactics has led to a continual interplay of measures and countermeasures in which no other conclusion retains its validity for very long. If this lesson alone is learned from it, the volume will have served a useful purpose.

The general organization corresponds closely to the dual aim described above, with two parts quite different in character. Part I is a historical summary of the progress of enemy submarine operations and Allied antisubmarine operations during World War II. No attempt has been made, however, to give a complete chronology of all events. The point of view is statistical, and every effort is made to describe the progress of World War II in quantitative and objective terms. The data are interpreted in terms of the ever-changing tactical and strategical situation. Accordingly, the historical summary is divided into seven chronological periods, as indicated in the Table of Contents. This division is necessary because of the radical changes in the nature of the U-boat war due to changes in U-boat tactics and the introduction of new weapons and countermeasures.

The periods were chosen in such a way that U-boat strategy and tactics were fairly homogeneous in each. The tactics of individual U-boats varied considerably, however, from the typical characteristics which were common to the operations of most of the U-boats during the periods in question. In particular the division points between periods are somewhat indefinite and represent the approximate dates at which a majority of the U-boats had made a major change in their methods of operation.

The data for a given period are further divided into three main sections.

  1. A chronological narrative of the most important activities and accomplishments of the U-boats and Allied antisubmarine forces.

  2. A more detailed account of the main Allied countermeasures to the U-boats, subdivided into

    1. Convoys
    2. Aircraft
    3. Scientific and technical
    4. Sinkings of U-boats.
    5. A survey of the results achieved during the period, from both the U-boats' and the Allies' point of view. This section attempts to explain the reasons for the new tactics which characterize the new period.

Part II of the volume is a more detailed analysis of certain of the major problems of ASW, in particular those which were the subject of operations research studies. The emphasis is on the evaluation of tactics and matériel both by theoretical analyses and by special studies of operational data. Although the principles of ASW derived from such evaluation are strictly applicable only to the situation which obtained during World War II, the methods of evaluation are of more general interest.

The U-boat war spread over all the oceans of the world, but the main battle was fought in the Atlantic. Consequently U-boat activity in other regions has not been discussed as completely as the Battle of the Atlantic. A standard subdivision into areas, which has been used throughout the text, is given in the frontispiece.

There are, in fact, many aspects of the war which are omitted from the discussion. The operations of midget submarines and small battle craft are generally excluded, since they are not considered U-boats. The importance of the training of personnel and developments along this line are not considered. The activities of Naval Intelligence in obtaining information upon which operations are planned are not described


in any detail. The indirect effects of factors such as strategic bombings are largely neglected. The net result is to limit the discussion fairly closely to Navy antisubmarine operations, though Royal Air Force Coastal Command aircraft and those of the United States Army Air Forces are included when flying antisubmarine missions. The distinction is not a hard and fast one.

The sources of material used are so widely scattered through correspondence and informal memoranda that it has not been practical to quote references to them.

In addition, numerous letters, notes, informal memos, and even oral conversations go to make up the background of this volume. One of it's chief aims has been to set down in writing a fair sample of this store of material whose previous status verged on that of folklore.

No effort has been made, therefore, to assign credit for the work discussed. It originates with various members of British and United States operations research groups, military services, and civilian war agencies. We have tried to collect available information and tell a reasonably unified story, not of the accomplishments of a particular group, but of the progress of a special type of Naval Warfare.




Chapter   Page
1 First Period--Submerged Daylight Attacks on Independents, September 1939--June 1940 3
2 Second Period--Night Surfaced Attacks on Convoys, July 1940--March 1941 8
3 Third Period--Start of Wolf Packs; End-to-end Escort of Convoys, April 1941--December 1941 16
4 Fourth Period--Heavy Sinkings on East Coast of United States, January 1942--September 1942 25
5 Fifth Period--Large Wolf Packs Battle North Atlantic Convoys, October 1942--June 1943 34
6 Sixth Period--Aircraft Defeat U-Boats' Attempted Comeback and Force Adoption of Maximum Submergence, July 1943--May 1944 44
7 Seventh Period--Schnorchel U-boats Operate in British Home Waters, June 1944--End of War 64
8 Summary of Antisubmarine Warfare, World War II 80
9 Safety of Independent Shipping 93
10 Convoying and Escort Shipping 100
11 Attacks by Surface Craft 113
12 Attacks by Aircraft 127
13 Offensive Search 139
14 Employment of Search Radar in Relation to Enemy Countermeasures 153
15 Countermeasures to the German Acoustic Torpedo 153
  Epilogue 177
  Appendix I 181
  Glossary 183


Transcribed and formatted for HTML by Rick Pitz for the HyperWar Foundation