When World War II began in Europe in the autumn of 1939, the "Altair" was tending Destroyer Squadrons 4 and 6, of Destroyer Flotilla 2, Battle Force, still based on San Diego. In March 1940, however, to service the destroyers of the Hawaiian Detachment sent to Pearl Harbor in December of the previous year, the "Altair" was shifted to Pearl. En route to her new duty station, she served as plane guard for Navy Consolidated PBY Catalina flying boats being ferried to Oahu, arriving at Pearl Harbor on 16 April 1940. She tended destroyers there through the end of the year 1940 and into 1941 as the fleet based permanently on Pearl Harbor following the conclusion of Fleet Problem XXI.