18 Japanese submarines active to the eastward of the line Yokosuka-Marshall Islands according to the U.S. Joint Intelligence Committee. Daily summary dated 12 January 1942

An item reported the estimated number of 18 Japanese submarines active to the eastward of the line Yokosuka-Marshall Islands. In the Hawaiian area were 5 submarines. Submarines active in the Hawaiian and west coast were presumably stationed at Jaluit [Marshall Islands] and Japan regarded the departures in westerly or southwesterly directions from submarines coming from the vicnity of Oahu.

Source

Map Room Papers (Roosevelt Administration), 1942 - 1945. U.S. Joint Intelligence Committee. Daily summary dated 12 January 1942 No. 33