US aircraft attacked harbour of Rabaul according to the U.S. Joint Intelligence Committee Daily summary dated 16 May 1942

An item reported the attack by US army bombers of 13 May on the ships lying in the harbour of Rabaul with a near miss on a transport. A day was a second attack possibly damaging a transport. The same day 3 heavy bombers attacked a Japanese transport on a distance of 20 miles south of Rabaul.

Source

Map Room Papers (Roosevelt Administration), 1942 - 1945. U.S. Joint Intelligence Committee. Daily summary No. 157 dated 16 May 1942