Ainsworth held numerous commands in the Pacific but he is remembered for his part in the Battles of Kula Gulf and Kolombangara. Ainsworth was in command of a task force of three cruisers and five destroyers which was escorting the invasion force to New Georgia. On 4-5 July 1943 his guns shelled Vila and Bairoko but he lost a destroyer in this action. On the night of 5-6 July Ainsworth’s force was patrolling the Kula Gulf when they ran into Japanese transports on a reinforcement mission to New Georgia. The ‘battle’ was very confused: the US ships did not stay in formation and one cruiser, the Helena, was sunk. It was thought that Ainsworth had repulsed the transports but the Japanese had landed on New Georgia.
On the night of 12-13 July Ainsworth took part in his fifteenth combat mission up the Slot, the channel dividing the Solomons in two. The US had the advantage of radar but the Japanese had an anti-radar tracking device. The Japanese were also equipped with ‘Long Lance’ torpedoes which had greater range and higher speed than US torpedoes. Ainsworth did not know of the potential of these torpedoes and was lucky to lose only one destroyer in this action. Ainsworth continued to serve in the Pacific and supported the amphibious operation in the Marianas. He retired in 1948.