"Ro-64" got underway from Kwajalein on 24 December 1941 to patrol off Wake Island, which had fallen to Japanese forces on 23 December 1941 in the Battle of Wake Island. She arrived off Wake on 27 December and then patrolled east of the atoll from 28 to 30 December 1941, when she made port at Wake. She departed Wake on 1 January 1942 and called at Truk in the Caroline Islands from 6 to 15 January before getting back underway in company with "Ro-63" and "Ro-68" to conduct a reconnaissance of Rabaul on New Britain in the Admiralty Islands. She then patrolled south of Cape St. George on New Ireland in support of Japanese forces landing at Rabaul before she returned to Truk on 29 January 1942.