Large scale W/T communication of Japanese fishing vessels according to the U.S. Joint Intelligence Committee. Daily summary dated 18 December 1941

An item referred to OPNAV reporting the receival of many RDF boarings and positions of positions of Japanese forces but searches discovered just fishing vessels. So it was possible that these vessels were practicing radio deception on station, contacting Japanese submarines or used as lookouts for Japanese naval forces.

Source

Map Room Papers (Roosevelt Administration) mr0422a. U.S. Joint Intelligence Committee. Daily summary No. 8 dated 18 December 1941.