Probably Japanese preparing an offensive in the Eastern Pacific according to the U.S. Joint Intelligence Committee Daily summary dated 15 May 1942

An item reported that the lack of Japanese naval activities probably indicated that preparations were made for an offensive in the Eastern Pacific before the end of the month.

Source

Map Room Papers (Roosevelt Administration), 1942 - 1945. U.S. Joint Intelligence Committee. Daily summary No. 156 dated 15 May 1942