Admiral Ainsworth believed he had inflicted severe damage on the Japanese at Kula Gulf and he was commendably eager to inflict more. The opportunity to do so came quickly enough. The American campaign to take Vila was not going well. Morison called it the “most unintelligently waged land campaign of the Pacific war.” Japanese reinforcements might have been enough to tip the balance and reinforcements were on the way. A “Tokyo Express” was scheduled for the night of July 12-13.
The Japanese force, commanded by Rear Admiral Izaki, consisted of a support group of one light cruiser and five destroyers and a transport group of four destroyer transports. These were: Support Group - light cruiser Jintsu, destroyers Mikazuki, Yukikaze, Hamakaze, Kiyonami and Yugure and Transport Group - destroyer transports Satsuki, Minazuki, Yunagi, and Matsukaze.
Ainsworth had been reinforced for this battle. He had light cruisers Honolulu, HMNZS Leander, and St. Louis; Destroyer Squadron 21 with Nicholas, O’Bannon, Taylor, Jenkins, and Radford; and Destroyer Squadron 12 with Ralph Talbot, Buchanan, Maury, Woodworth and Gwin.
Destroyer Squadron 12 with six vessels had been added to Ainsworth force, along with the Leander, to offset the attrition his force had suffered in its frequent forays up the Slot. These last minute additions had never operated with Ainsworth before. That a smaller, well-integrated group was more effective than a larger slap-together force was a lesson the Americans were a long time learning.
"Black Cat" PBY Catalina aircraft spotted the Japanese at 0036 at a distance of 26 miles. The Allies established radar contact at 0100 and visual contact three minutes later. Ainsworth’s had deployed his task force in a single column with five destroyers in the van followed by the cruisers and five destroyers in the rear. At this time the Allied force was heading west about twenty miles east of the northern tip of Kolombangara. The Japanese Support Group, also in a single column, was proceeding southeast about 12 miles off Kolombangara. Ainsworth was again complacently assuming he had complete surprise. In fact, Admiral Izaki had been aware of the Allied force for almost two hours. The Japanese had invented a useful device that sensed a radar’s electric impulse, apparently at a range greater than the radar itself was able to function. Izaki was able to use this device in its first operational test to accurately plot the approach of the Allied task force. At 0106 Ainsworth turned the cruisers 30° right to unmask their main batteries while ordering the lead destroyers to increase speed. The van destroyers began launching torpedoes at 0110 at a range of 10,000 yards. The Japanese beat them to the mark by two minutes, launching torpedoes between 0108 and 0114. Izaki then turned his column almost directly north.
Jintsu snapped on her searchlight as the torpedoes got underway and opened fire. Honolulu closed to 10,000 yards and the Allied cruisers replied at 0112. The Allies had spotting aircraft overhead as well as radar direction. As usual, all fire was concentrated on the largest ship. In eighteen minutes between 0112 and 0130 Jintsu was the unfortunate target of 2,630 6” and 353 5” shells. She was dead in the water by 0117 when she was hit by an American torpedo.
At 0117 Ainsworth ordered a turn to the south. Leander turned wide and caught a torpedo at 0122, suffering severe damage. Given the number of torpedoes fired by the Japanese, the Allies were fortunate she was the only ship hit during this portion of the battle. Leander retired from the battle, working up to 10 knots, escorted by Radford and Jenkins.
Mikazuki apparently stayed by Jintsu to assist her while the other four destroyers sped north, then northwest, passing through a rainsquall along the way. By 0136 they had finished reloading their torpedo tubes and turned back to the southeast, ready for more action. At 0131 Ainsworth dispatched Nicholas, O’Bannon and Taylor to chase them. They didn’t make it very far, sending more torpedoes into the two burning halves of Jintsu at 0138 and finishing her off. They were about 20,000 yards west of the main American force at this time. Ainsworth had a decision to make. As usual, he believed he had done very well, sinking between three and six ships and probably crippling the balance. Rather than turn for home as the fortunate victor in a sharp action, he elected to bend a course northwest at 30 knots and finish off the imaginary cripples.
At 0156 Honolulu’s radar picked up a group of ships at a range of 23,000 yards. Unfortunately, Ainsworth was not clear where his three detached destroyers were. He spent several minutes trying to determine their location. At 0205 he had the unknown ships illuminated with star shell and observed they were turning away as if they had just fired torpedoes. They had. The radar detection device on Yukikaze had alerted them to the presence of the American ships by 0157.
Ainsworth ordered a 60° turn to port to unmask guns and ordered open fire, but, at 0208 before this order could be obeyed, St. Louis was struck by a torpedo in her bow. Honolulu dodged several others, but was hit in the same place at 0211, and by a dud in her stern. At 0214, Gwin took one amidships and exploded. Ralph Talbot was the only American vessel to take any action during this portion of the battle, ineffectively sending torpedoes after the fleeing Japanese at 0213.
Gwin was scuttled at 0930 the next morning. Honolulu and St. Louis were out of action for several months, returning to Pearl Harbor for new bows, and then to Mare Island for refitting and replacement of their antiair armament. Leander had to go all the way to Boston and was under repair for a year. She never returned to action. Except for Jintsu, the Japanese force completely escaped damage. The Transport Group successfully landed 1,200 men on Vila. In every respect, this battle was a major defeat for the Allies.