TheCodeBreakers
communications. Hence the Navy relied increasingly on it for its
information on Japanese naval activities as security tightened in Japan
during 1941, and almost exclusively after July, when the President's
trade-freezing order deprived the Navy of all visual observations of
Japanese ships not on the China coast.
It was in July that a Japanese tactic set up a radio pattern that was
later to deceive the Combat Intelligence Unit. The Nipponese militarists
had decided to take advantage of France's defeat and occupy French
Indochina. The Naval preparations for the successful grab were clearly
indicated in the radio traffic, which went through the usual three stages
that preceded major Japanese operations. First appeared a heavy flurry
of messages. The Commander-in-Chief Combined Fleet busily originated
traffic, talking with many commands to the south, thereby indicating the
probable direction of his advance
annaabi.ee 
