Japanese submarines active in the Bay of Bengal according to the U.S. Joint Intelligence Committee. Daily summary dated 9 April 1942

An item reported that another two British merchant ships in the Bay of Bengal were attacked by Japanese submarines. The J.I.C. commented that minimal 7-8 Japanese submarines were active in the North Indian Ocean including the Bay of Bengal and the Arabian Sea. The submarines were mostly seen in the area south-west of Colombo where the most ships were torpedoed and sunk.

Source

Map Room Papers (Roosevelt Administration), 1942 - 1945. U.S. Joint Intelligence Committee. Daily summary No. 120 dated 9 April 1942