Transferred to command of TF 18 and Cruiser Division 9 (CruDiv 9), Ainsworth continued his success during a prolonged series of runs up the long, narrow body of water between the central Solomon Islands which American bluejackets had nicknamed "the Slot". These operations parried the thrusts by Japanese warships challenging Allied control of the area. At the end of June, the tempo of American fighting in the southwestern Pacific picked up since the Navy had finally managed to assemble enough amphibious shipping in that theatre to resume the offensive. On the night of July 4–5, TF 18 moved up "the Slot" and bombarded Japanese positions at Vila on Kolombangara and at Baiko on New Georgia. The next afternoon, while Ainsworth's force was retiring from this action, word reached him that a large Japanese force was heading toward "the Slot". In an effort to meet and check this new threat, his warships again reversed course and headed toward the enemy. Ainsworth's "... outstanding leadership, brilliant tactics and courageous conduct ..." in the ensuing battle of Kula Gulf won him a Navy Cross. He also received the Distinguished Service Medal for his overall performance in the Southwest Pacific.