I have Enigma by Hugh Sebag-Montefiore (https://www.amazon.com/Enigma-Battle-Code-Hugh-Sebag-Montefi...) except in incredibly nice Folio Society edition. It is meticulously researched and covers all the fun parts of Bombes and programming. The appendixes do step by step algorithm explanation of how this work. Tons of unsung heroism in the seas with the capture of various machines from U boats and ships.