This book is an edition of the General Report on Tunny with commentary that clarifies the often difficult language of the GRT and fitting it into a variety of contexts arising out of several separate but intersecting story lines, some only implicit in the GRT.

• Explores the likely roots of the ideas entering into the Tunny cryptanalysis
• Includes examples of original worksheets, and printouts of the Tunny-breaking process in action
• Presents additional commentary, biographies, glossaries, essays, and bibliographies