To err is human vol2

In ‘German special intelligence, the M-138 strip cipher and unrest in India’ I had said that the Western Allies were able to monitor the exchange of information on Allied codes and ciphers between Germany, Finland and Japan thanks to their solution of the Japanese Coral cipher machine. This was not correct.

Ralph Erskine pointed out to me that the Coral was mainly used by Japanese naval attaches and that the relevant histories of this system do not mention it being used for transmitting Allied cipher material. Further research at the US National Archives and Records Administration revealed that the code used for transmitting solved Allied cipher material was JAT, a letter code used together with a Gronsfeld square and a book containing random 4-figure groups.  

I’ve corrected the relevant passage in my essay and added scans from the document ‘JAT write up - selections from JMA traffic'.