Let me wholeheartedly echo John's recommendation; this is a terrific book, one from which I learned a great deal. You'll get more out of it, however, the more you already know about the Bletchley Park efforts and the principles on which the Enigma and Lorenz machines operated. In particular, Welchman's "The Hut Six Story" (McGraw Hill, 1982) makes good preparatory reading. Unfortunately, that book has been out of print for some time, but is fairly widely available at used book shops. I had the opportunity to visit Bletchley Park a couple of weeks ago. Most of the original huts are still standing, albiet in various states of disrepair. Walking around the site, knowing something of what went on there in complete secrecy 50 years ago, I could only imagine the sense of urgency and bustle that must have been in the air with 12000 people working (day and night, over three shifts) in a relatively small space. The more I learn about the effort the more impressed I am with the accomplishments that took place there. In particular, the path from basic research to operational functionality was far shorter than one would think possible. After the war, the site was used by GCHQ and by British Telecom as a training center. It was recently saved from redevlopment and is now being converted into museum. Among the projects taking place there is a construction of a working model of the original "Colossus" machine, arguably the first electronic computer ever built (it was used in breaking the Lorenz teleprinter cipher). I believe the site is currently open for visitors on alternate weekends. -matt