With the failure to capture Port Moresby due to the battle of the Coral Sea and the subsequent return of the invasion force to Rabaul, the South Seas Detachment-led by Major General Tomitarō Horii-was attached to the 17th Army.
The Imperial Japanese Navy 4th Fleet provided naval support including Cruiser Division 18 led by Rear Admiral Kôji Matsuyama consisting of and , Destroyer Division 29 consisting of , and , and the transports , Kinryu Maru and .