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The Communications Intelligence Unit (CIU) was part of Admiral Husband E. Kimmel's CinCPAC responsibility and was commanded by Commander Joseph Rochefort. The main interest of this unit was the penetration of Japanese Naval communications, encoded using JN-25. As they had not, as it is alleged Eric Nave (Nave, Eric) and FECB had, broken the code most of their work was on traffic analysis. This involved recording and interpreting the numbers and places of origin of messages to work out what was going on. The unit could well have decoded the consular messages that Japanese espionage was generating from Honolulu and thus could have gathered that an attack was planned, but, like their counterparts in Washington, they assigned low priority to consular traffic. The work of CIU did give some warning of Operation K, another attack on Pearl Harbor in March 1942 by two Japanese aircraft.

See also: CinCPAC; espionage; FECB; JN25; Nave, Eric; Operation K; Pearl Harbor