Japanese naval forces leaving Bay of Bengal according to the U.S. Joint Intelligence Committee. Daily summary dated 17 April 1942

An item reported that the center of Japanese offensive naval activity was leaving the Bay of Bengal. The departure of the aircraft carriers was first blamed to the losses of aircraft, but it became clear that 3 were to operate elswhere. Cruisers were also leaving but perhaps staying nearby. In the afternoon of 15 April sighted the R.A.F. a Japanese battleship (perhaps a cruiser) and a destroyer on a distance of around 100 miles south of Ceylon. According to British sources there were maximum 3 battleships, 2 aircraft carriers, 3 heavy cruisers, 3 quadrons of destroyers and 3 squadrons of submarines in Malayan waters. Despite the Japanese navy withdrew warships of the Bay of Bengal large numbers of merchant types entered the area. Allied merchant shipping from the Calcutta southward remained suspended due to Japanese naval forces in the vinity of Ceylon.

Source

Map Room Papers (Roosevelt Administration), 1942 - 1945. U.S. Joint Intelligence Committee. Daily summary No. 128 dated 17 April 1942