The American Magic: Codes, Cyphers, and the Defeat of Japan
The American Magic isn't about how Japan's codes were broken; it's about how the U.S. used that information. It's largely book for specialists. Some of the information is interesting, but none of it is revelatory at this late date, and it's not presented with the narrative verve that would make it generally accessible. The details of how the various bureaucracies were organized, for example, is important but not exactly page-turning.
The most entertaining bits come when Lewin takes a few full-arm swipes at Douglas MacArthur (who, incredibly, still has star-struck hero-worshipers writing adoring books about him). Otherwise, this is a book for people with both a good working knowledge of the history of the Pacific War and a substantial investment in the subject matter.