Japan maintained several naval bases in the Solomon Islands according to the U.S. Joint Intelligence Committee. Daily summary dated 25 August 1942

An item reported that the Japanese forces used Tonolei Harbor (S.E. Bougainville Island), Buin (Bougainville Island) and Faisi (Shortland Island) all in the Solomon Islands. On 23 August were at least in the area sighted 2 Japanese heavy cruisers, 1 seaplane tender, 5 destroyers, 1 large tanker and 3 other ships. Further more 2-3 heavy cruisers, at least one small aircraft carrier and several destroyers seen 250 miles of Guadalcanal Island. The J.I.C. commented that the Japanese used the Faisi-Buin-Tonolei area as an advance base for the Solomon Islands.

Source

Map Room Papers (Roosevelt Administration), 1942 - 1945. U.S. Joint Intelligence Committee. Daily summary No. 258 dated 25 August 1942.