TheCodeBreakers
consisted of weather and other minor systems. The information obtained,
Rochefort said, "was not in any sense vital." Cavite was spottily reading
JN25 messages—which revealed nothing about Pearl Harbor—until
December 4, when the superencipherment was suddenly changed. As a
message that moved on the monitor channel put it: "Five numeral
intercepts subsequent to zero six hundred today indicate change of
cipher system including complete change differentials and indicator
subtracters X All intercepts received since time indicated checked against
all differentials three previous systems X No dupes." Corregidor was not
to get the initial break into the new superencipherment until December
8. And the only other system in which the Yoshikawa messages might
have been forwarded—the flag officers' system—remained unsolved.
A possibility of warning was opened at the source, however, when
Yoshikawa's original messages became available to Rochefort's unit.
annaabi.ee 
