At the time of the attack on Pearl Harbor, Isonami was assigned to Destroyer Division 19 of Desron 3 of the IJN 1st Fleet, and had deployed from Kure Naval District to the port of Samah on Hainan Island. From 4 December 1941 to 30 January 1942 Isonami was part of the escort for the heavy cruisers Suzuya, Kumano, Mogami, and Mikuma out of Samah and Camranh Bay, French Indochina in support of Malaya, Banka-Palembang and Anambas Islands invasion operations.