David Kahn is the author of The Codebreakers, the most comprehensive text ever written on the history of cryptography. This book is taken as canon and reference to anything relating to the history of cryptography or cryptanalysis. He went to Oxford University, recieving a Ph.D in Modern History. He also wrote 'Kahn on Codes', 'Hitler's Spies', and 'Seizing the Enigma'.

I recommend 'The Codebreakers' only for those seriously interested in the field; the $65.00 price tag and scholarly style make it of little interest to the casual reader, though it is indispensible to anyone involved deeply in the field.

However, 'Siezing the Enigma' is written in a much more reader-friendly style, and recounts many exciting tales of the cipher battles of World War II, especially in the Battle of the Atlantic. I would highly recommend it to anyone with even a passing interest in history or cryptography.