For Keith Willshaw...

"Denyav" wrote in message
...
told the receiver what random numbers were used. Helps explain why
the USN had less than 10% of the book after 4 months.

So that means in April 1941,at the latest,US had 10% of the book in the
hand.
Can you tell us the percentage of the book available to US on Dec.4,1941?


Of the 50,000 code groups used only 3800 had been cracked

Or did US stop recovery work in April and started hibernating?

Nope the Japanese imtroduced a new 50,000 group additive
book in August 1941 which set them back months

They also had low priority, Joe Rochefort recorded that his group had
little
equipment, the tabulating machines and teletypes needed had been
diverted to the efforts to break the German and Italian codes and
the Japanese diplomatic cipher

He didnt even have a secure comms line to the radio intercept
station. All intercepts had to be delivered by courier. It wasnt
until Febuary 1942 that the group began to read even a small
portion of messages in JN-25

Keith