Gordon W. Prange, At Dawn We Slept
Gordon W. Prange, At Dawn We Slept
Thomas E. Griess, Series Editor, The Second World War: Europe and the Mediterranean
"Okuda swung into his espionage quickly and efficiently.
For a time, as Gunji had predicted, checking on Fleet movements presented no special problems.
The local press reported them faithfully, and Okuda extracted the germane items, coded them, and sent then to Tokyo by commercial telegraph.
What was public information in Hawaii became classified as soon as it reached the Foreign Ministry, which immediately relayed it to the Naval General Staff.
There it all became grist for the intelligence mill."
US code breakers had long since broken Japanese diplomatic codes, and understood what was being reported.
IIRC, similar information was reported on other US naval bases.