At the time of the attack on Pearl Harbor, "Myōkō" and "Nachi" formed "Sentai"-5 of the IJN 3rd Fleet. "Sentai"-5 was commanded by Rear Admiral Takeo Takagi, and deployed from Palau cover for the landings of Japanese forces under "Operation M" — the invasion of the southern Philippine Islands. After covering the landings of Japanese forces at Legaspi on 11 December 1941. "Myōkō" and "Nachi" returned to Palau and were then reassigned to the Rear Admiral Raizō Tanaka, whose attack force covered landings at Davao on 19 December and Jolo on 24 December.