For more info on JN25 and the mathematical model that William Friedman
wrote for building the decoding machine (Purple), see David Kahn's "The
Codebreakers".

Regards,

Marv

Peter H. wrote:

They explained how they broke the Japanese code.


The JN25 code was cracked by the Americans, at Pearl Harbor.

Perhaps a much lower level code, the Japanese Merchant's Code was cracked at
B.P.