三川軍一
On 14 July 1942, in a major reorganization of the Japanese navy, CruDiv 18 under Rear Admiral Mitsuharu Matsuyama came under the newly created IJN Eighth Fleet, commanded by Vice Admiral Gunichi Mikawa and based at Rabaul. On 20 July, "Tatsuta" was assigned to cover Japanese troop landings in the invasion of Buna, New Guinea ("Operation RI"). The invasion force was attacked by USAAF B-17 Flying Fortresss and B-26 Marauder bombers on its return to Rabaul, but "Tatsuta" was unharmed. "Tatsuta" escorted three more convoys to Buna in August, two of which were successful.