[172]   Communication Intelligence Summary, 1 December 1941
 
General.-All service radio calls of forces afloat changed promptly at  0000, 1 December. Previously, service calls changed after a period of  six months or more. Calls were last changed on 1 November, 1941. The  fact that service calls lasted only one month indicate an additional  progressive step in preparing for active operations on a large scale.  For a period of two to three days prior to the change of calls, the bulk  of the radio traffic consisted of dispatches from one to four or five  days old. It appears that the Japanese Navy is adopting more and more  security provisions. A study of traffic prior to 0000, 1 December  indicates that an effort was made to deliver all dispatches using old  calls so that promptly with the change of calls, there would be a  minimum of undelivered dispatches and consequent confusion and  compromises. Either that or the large number of old messages may have  been used to pad the total volume and make it appear as if nothing  unusual was pending.
First Fleet.-Nothing to indicate that this fleet as a fleet is operating  outside of Empire waters. It is believed that such a large percentage of  the First Fleet is operating with the Second Fleet Task Force that this  fleet has ceased to operate in a prominent role.
Second Fleet.-This fleet is believed proceeding from the Kure-Sasebo  area in the direction of South China and Indo-China. Takao does not  appear to play an important role in today's traffic; consequently, the  assumption is made that his fleet is passing up Takao. Certain units of  the Second Fleet Task Force are definitely in the Indo-China area  (Cruiser Division Seven and Destroyer Squadron Three most prominent).
Third Fleet.-Nothing to report except that the same association of  Second, Third Fleets, and Combined Air Force with South China and Indo- China Forces continues.
Fourth Fleet.-No change in the Fourth Fleet or Mandates area.
Fifth Fleet.-Nothing to report.
Submarines.-Large number of the Submarine Force believed to be in the  area to the eastward of Yokosuka-Chichijima and Saipan Flagship  somewhere in this general area.
Carriers.-No change.
Combined Air Force.-No change.

 

(FROM: U.S. CONGRESS JOINT COMMITTEE ON PEARL HARBOR ATTACK HEARINGS; PT.  35, THE CLAUSEN INVESTIGATION, PP. 62-81. EXHIBIT "A" DAILY COMMUNICATION INTELLIGENCE SUMMARIES)