ブーゲンビル島沖海戦
Ijuin saw no direct combat during the early months of World War II. However, on his promotion to rear admiral on 1 November 1943, he commanded DESRON-3, based at Rabaul, New Britain during the Solomon Islands campaign. He was the main Japanese commander at the minor Battle off Horaniu and larger Naval Battle of Vella Lavella, during which time he successfully evacuated the 600 man Japanese garrison from the island of Vella Lavella, while repulsing attacks by American naval forces under Admiral Frank R. Walker on 6–7 October 1943. Leading screening forces from the cruiser during the Battle of Empress Augusta Bay on 2 November 1943, Ijuin survived the sinking of "Sendai" and was later rescued, along with a few other survivors, by submarine .