The combined force, under Brown, stood toward Rabaul until the Japanese landings at Lae and Salamaua, New Guinea prompted a change of plans. Late on 8 March, Brown and his staff decided to shift objectives and attack the two new enemy beachheads by launching planes from the Gulf of Papua in the south and sending them across the width of New Guinea to the targets on the northern coast. "Astoria", meanwhile, joined a surface force made up of heavy cruisers "Chicago", "Louisville", and , and destroyers "Anderson", "Hammann", , and "Sims" under the command of Rear Admiral John G. Crace, that Brown detached to operate in the waters off Rossel Island in the Louisiade Archipelago. The heavy cruiser and the other warships of that force carried out a threefold mission. They secured the carriers' right flank during their operations in the Gulf of Papua; they shielded Port Moresby from any new enemy thrust; and they covered the arrival of Army troops at Nouméa.