At the time of the attack on Pearl Harbor, "Isuzu" was participating in the invasion of Hong Kong, as part of the 15th Escort Squadron in Vice Admiral Kiyoshi Hara's Second China Expeditionary Fleet. "Isuzu" remained based in Hong Kong after its capture by Japan from the end of December 1941 to April 1942, returning briefly to her home port of Mako, in the Pescadores to escort reinforcements for the Japanese 25th Army to Singora, Thailand and Camranh Bay, French Indochina