By the way I'm not in the "Roosevelt knew" school. Though, God forbid, one must believe the old fox was capable of devious methods.
All of the Prange stuff ("At Dawn We Slept" ...)... errors and all
The Howeth tome on the US Navy Electronics ... especially for radio, unilateral RDF procedures, intra-fleet simultaneously receive(on one frequency)-rebroadcast(on another frequency, ..., for US Navy capabilities in 1941,
Prados' "Combined Fleet Decoded"
Farago's "The Broken Seal" - importantly here - the paperback edition, especially the POSTSCRIPT section
Layton ... you have that ... and its errors and all,
Stinnett's "Day of Deceit" - again the paperback ... and yes, errors and all,
Wilford's "Pearl Harbor Redefined" - paperback ... and yes, there to, errors and all,
All of the Hearings ... Roberts, ... Thurmond/Spense.
The Pre-Pearl Habor Japanese Dispatches ... say the Navy's copy ... Naval Historical Center ... yes, errors and all.
Those should keep you busy on radio silence for starters ... much more adds to that.
On the codes ... please ask LS ... Oh, start with Kahn's seminal "The Codebreakers" ... yes, errors and all. For the "trade" magazine try "Cryptologia" ... again, just a start ...
I hope that helps ...
[Oh, yes, the Kido Butai broke radio silence ... known then and known now. With those sources above we can piece together exactly how it was done. It might also explain why so much Pearl Harbor material remains locked up in Navy vaults (e.g., Mid-Pacific RDF logs, ...) and beyond FOIA actions.
Why do you suspect the details on this AKAGI message are so radioactive?
Posit or imagine ... the timing of this summary, and what it would have taken to write it ... intercepting some traffic (time of day, frequency, signal characteristics, ... RDF bearings perhaps, ... decoding the traffic ... the code used was ... and it was read when ..., etc.]