Two very interesting reports detailing the main Japanese diplomatic and naval cryptosystems of WWII are available online via the Australian National Archives website.
To view the reports go to the National Archives site, click on ‘RecordSearch’, then click Advanced search for items and next to ITEM BARCODE enter 12127133 for the diplomatic report or 859305 for the Naval report.
1). The first report is titled ‘Special Intelligence Section report - Japanese Diplomatic ciphers’ and covers the codes and ciphers used by Japan’s Foreign Ministry, their characteristics and the success that the Anglo-American codebreakers had with each one.
2). The second report covers the codes and ciphers of the Imperial Japanese Navy and it is titled ‘Volume of technical records containing details of codes and cyphers’. The unofficial title is ‘The Jamieson report’.
Note that one of the systems mentioned is the JN-87 strip cipher. The Japanese thought so highly of the US M-138-A strip cipher that they copied it and used it with certain modifications!
Acknowledgements: I have to thank Professor Peter Donovan for informing me of the ‘Jamieson report’.