Japanese losses of ships limitated number of agressing moves according to the U.S. Joint Intelligence Committee. Daily summary dated 15 April 1942

An item referred to a statement of Australian authorities claiming that the Japanese losses of ships were such heavy that only one agressive move at a time could be supported. When they extended their theater of operations even further including more shipping losses their problems would became such precarious that they could just hold and defend the occupied area.

Source

Map Room Papers (Roosevelt Administration), 1942 - 1945. U.S. Joint Intelligence Committee. Daily summary No. 126 dated 15 April 1942.