Joined by two destroyers from Tulagi, Ainsworth headed back, arriving off the entrance an hour after midnight. The sky was overcast, there were passing showers, and visibility was 2,000 yards or less. Radar contact was made at 1:36 a.m. on 6 July with three warships some 22,000 yards distant, standing out of the gulf 5,000 yards off the Kolombangara shore. Ainsworth immediately assumed battle formation: two destroyers in column ahead; the light cruisers Honolulu, Helena, and St. Louis behind them; and two destroyers astern. At the same time, Ainsworth turned left to close with the Japanese, and then, at 1:49, he came back right to unmask all guns. Radar then picked up a second Japanese group astern the first, and Ainsworth delayed opening fire as he pondered this new situation.
The Japanese were, in fact, in three groups. The first, with which Ainsworth had made contact, was Rear Admiral Akiyama Teruo's covering force of the destroyers Niizuki (flag), Suzukaze, and Tanikaze. The second group was made up of four destroyer-transports that Akiyama had first ordered to make for Vila; when contact was made with Ainsworth, he directed them to reverse course and join in the battle. The third group of three destroyer-transports was already unloading at Vila.
Ainsworth opened fire on the Akiyama's group at 1:57 a.m., and the rapid-firing, radar-directed 6-inch guns in which the Americans put their faith quickly hammered the Niizuki into a wreck. But the gunfire lit up the American battle line, and almost immediately, the Suzukaze and Tanikaze launched 16 torpedoes and escaped to the northwest. Believing that he had accounted for all three ships of Akiyama's group, Ainsworth countermarched at 2:03 a.m. to deal with the transport group. Seconds later, three Japanese Long Lance torpedoes struck the Helena. She sank about 2:25. At 2:18 a.m., Ainsworth took the transport group under fire, scoring some hits, but the four destroyers scattered and headed for Vila, the only casualty resulting when the Nagatsuki ran hard aground on Kolombangara.
Finding no targets to the west and convinced that he had accounted for many more Japanese ships than the Niizuki, Ainsworth, whose own ships were low on both fuel and ammunition, ordered his force to head for Tulagi, leaving the Nicholas and Radford to pick up the Helena's survivors. Three times during the early morning hours, the two destroyers interrupted their work to engage Japanese ships. Although gunfire and torpedoes were exchanged, there was no major damage to either side, and by daylight, Kula Gulf was clear of the Japanese vessels.
Dull, Paul S. A Battle History of the Imperial Japanese Navy (1941–1945). Annapolis, MD: Naval Institute Press, 1978.; Morison, Samuel Eliot. History of United States Naval Operations in World War II. Vol. 5, The Struggle for Guadalcanal, August 1942–February 1943. Boston: Little, Brown, 1949.