American submarine sunk a Japanese merchant ship off Japanese coast according to the U.S. Joint Intelligence Committee. Daily summary dated 9 January 1942

An item reported that Japan admitted that an American submarine sunk a Japanese merchant ship about 100 miles south east of Yokohama, Japan. The J.I.C. commented that it was the first indication that American submarines were active in the vicinity of Japan.

Source

Map Room Papers (Roosevelt Administration), 1942 - 1945. U.S. Joint Intelligence Committee. Daily summary No. 30 dated 9 January 1942