Japanese navy quite active around Bougainville Island according to the U.S. Joint Intelligence Committee. Daily summary dated 2 April 1942

An item reported that the Japanese navy was quite active in the northern Solomon Islands especially around Bougainville Island. There were numerous naval vessels including heavy cruisers seen in the past few days. It was believed that the Japanese were preparing an offensive to the southeast of the Solomon Islands or screening shipping activity at Rabaul, New Guinea.

Source

Map Room Papers (Roosevelt Administration), 1942 - 1945. U.S. Joint Intelligence Committee. Daily summary No. 113 dated 2 April 1942