American submarine damaged Japanese tanker and sunk sea plane tender according to the U.S. Joint Intelligence Committee. Daily summary dated 18 August 1942

An item reported that an US submarine claimed damaging of a 6,000 ton tanker on 3 July and sinking 3 days later a Japanese converted seaplane tender similar to the Soyo Maru of 6,081 gross tonnage, both attacks found place in the vicinity of the Marshall Islands.

Source

Map Room Papers (Roosevelt Administration), 1942 - 1945. U.S. Joint Intelligence Committee. Daily summary No. 251 dated 18 August 1942.