This 416-page book by Peter M.A. Donovan and Richard J. Aldrich reveals how Allied code breakers evolved techniques to break Japanese Navy and Army codes during World War 2, which helped plan battles and submarine attacks in the Pacific. It traces the development of cryptanalysis methods used to solve the main Japanese Navy code and Water Transport Code. The book also explores the organization of code breaking teams and issues of security and censorship. It aims to close remaining gaps in understanding how signals intelligence was crucial to Allied planning throughout the war.