At the time of the attack on Pearl Harbor in 1941, Iwabuchi was captain of the seaplane tender . He was reassigned to the staff of the Combined Fleet on 25 March 1942, and was subsequently given command of the battleship on 20 April 1942. However, "Kirishima" was sunk at the Second Naval Battle of Guadalcanal on 15 November of the same year. A week later, on 22 November, Iwabuchi was reassigned to command the 11th Air Fleet in charge of air operations over Guadacanal and Rabaul.