Open up the can of worms...

The Ludwig von Mises Institute ^ | May 26, 2001 | Lawrence Reed

[GATOR NAVY]

I'm still pretty sure by Dec 1941, the code most penetrated was purple. You're right, JN-25 was being read at this point, but not the extent purple was. And all I've read said the Japanese transmitted by radio nothing of their plans for Pearl Harbor except the execute signal. Everything else was hand carried or telephoned to those who needed to know, which means even if we were reading 100% of their transmitted traffic, there would have nothing for us to intercept in the first place.

[GATOR NAVY]

And is it fate I'm career Navy? My birthday is Dec 7, 1961. Twenty years to the day...

[GATOR NAVY]

As to radio signals, there were intercepts of the Japanese warships calling up oilers for refueling

I believe the oilers were in company with the strike force, therefore there would have been no need to call them up. In fact the only concerns about refueling were weather related.

[Jimmy Valentine]

If you read the book, you will see that contrary to the "legend" the Japanese radio discipline was quite poor.