Seizing the enigma: The Race to Break the German U-boat Codes, 1939-1943

This 1991 book tells about the secret history of the Battle of the Atlantic, between Allied shipping and Nazi submarines. The German Navy used a version of Enigma that defied code breakers in the early years of the war. After key documents were captured by the British, they were able to decode the messages. This book tells this story in about 360 pages, with an index and bibliography. The 'Preface' lists the acknowledgments. The Battle of Britain failed to defeat the British, next came the Battle of the Atlantic to destroy supply ships. The British used ASDIC and RADAR to detect submarines, but this had a limited range. Only decoded German naval messages would locate the submarines, and allow a convoy to avoid them. The U-boats were controlled by radio from France with constant communication. When a damaged U-boat surfaced, the captain of the attacking British destroyer decided to board it and capture its codebooks. Chapter 3 tells of the history of the Enigma cypher machine. Necessity is the mother of invention. Chapter 4 tells how this perfectly unbreakable system began to be broken: it use by imperfect men (p.69). The prohibition against keys with repeated letters provided a guide to cryptanalysts (p.70)! Chapter 7 reminds us that intelligence is secondary to strength (p.91). The sinking of U-33 led to the recovery of three rotors (p.111). Since small German ships did not use Enigma but a code known to the British, the latter were used to decode the former (p.144). The capture of the U-110 and its Enigma, ocean charts, and coding keys was priceless (Chapter 13). The capture of a weather ship brought a new supply of key settings (Chapter 14). Warnings of U-boats saved convoys (Chapter 15). Capturing a cipher book from the U-559 allowed breaking the new four-rotor code (Chapter 19). Chapter 20 tells how one convoy evaded U-boats. The cavity magnetron allowed ultra-high frequency radar which could not be detected by U-boats (Chapter 21). The Nazis believed this explained the Allies' success (p.261). The operational efficiency of U-boats was improved by having them resupplied at sea by special submarine tankers (Chapter 22). Sinking one reduced the effectiveness of many U-boats. The use of escort carriers allowed active attacks on U-boats, not just defensively (p.267). Sinking these supply ships and U-boats won the Battle of the Atlantic. ULTRA was the greatest secret of World War II (p.276). It could both avoid the enemy, and lead to an attack, with a minimal force. Another important factor was the huge production from American shipyards and aircraft factories. [Unmentioned is the war on the Eastern front, which required most Nazi military forces.] The British and Americans used a five or ten rotor machine with a more complex motion; and total censorship of this (p.279). The motivation for intelligence is described on pages 280-281. Another factor for efficiency was that American and British forces cooperated, while Germany had seven major code-breaking agencies that operated separately. A similar comparison could be made to the intelligence agencies. The British were unified, the Germans had competitive agencies. This book provides a short history, but I think it omitted areas for space considerations.