Another eye-opener for the farmer's daughter. What would I know. Too many years spent watching films and not reading the 'right' books. Films told me, the mathematicians at Bletchley built a computer and used that to crack the German's codes. Not true.
This book tells the story of the Polish breaking of the German Enigma code before WWII and thru the early part of the war. The famous English Enigma work was based on the earlier work performed by 3 Polish mathematicians. This book tells how the Polish broke the code using mathematics (not a captured machine as is commonly thought) and details the methods used to decrypt messages when settings were changed. There is a lot of (Polish) patriotic pride in this book which occasionally gets in the way of the content, but it is an excellent book nonetheless. It includes an appendix in which the mathematician who originally broke Enigma explains exactly how he did it which is especially interesting.