The 'Battle of Kolombangara', which is otherwise known as the '2^nd Battle of Kula Gulf', was a naval battle fought between US and Japanese naval forces off the north-eastern coast of Kolombangara in the Solomon islands group (12/13 July 1943).

The battle took place during the early stages of the US 'Toenails' invasion of New Georgia after an Imperial Japanese navy force, carrying reinforcements south to Vila, at the southern end of Kolombangara island just to the north of New Georgia island, was intercepted by a task force of US and New Zealand light cruisers and destroyers. In the ensuing action, the Japanese sank one Allied destroyer and damaged three cruisers, and were also able to land 1,200 ground troops on the western coast of Kolombangara island, but in the process lost one light cruiser sunk.

The invasion of New Georgia had begun on 30 June as part of the Allied 'Cartwheel' advance through the central part of the Solomon islands group toward the main Japanese base area round Rabaul on New Britain island. In the initial phase of the operation, Rendova had been captured to provide a staging point for US forces tasked with capturing the Japanese airfield at Munda Point, which was one of the campaign’s key objectives. On 2 July 1943, troops of Major General John H. Hester’s US 43^rd Division landed on New Georgia to attack Munda, while three days later a battalion of US Marine Raiders and two US Army battalions were landed at Rice Anchorage on New Georgia’s northern coast to seize Bairoko.

In response to the US landings, the Japanese sought to reinforce New Georgia as a means of bolstering the southern flank to their base area around Rabaul. On the night of 12 July, a Japanese 'Tokyo Express' naval reinforcement force made a run down 'The Slot' from the Rabaul to land troops at Vila on Kolombangara by way of the Kula Gulf. This force was commanded by Rear Admiral Shunji Isaki and consisted of the light cruiser Jintsu, the destroyers Mikazuki, Yukikaze, Hamakaze, Kiyonami and Yugure as well as the destroyer transports Satsuki, Minazuki, Yunagi and Matsukaze. These latter four ships carried 1,200 ground troops, which were to be landed on Kolombangara. The ships of Isaki’s force had been drawn from a number of different numbered elements, but the core was formed by Destroyer Squadron 2.

The movement of the Japanese ships was detected and reported by Allied coastwatchers, and in response Admiral William F. Halsey, commanding the South Pacific Area, ordered a naval task force to intercept the Japanese ships. Designated Task Force 18, the Allied naval force was commanded by Rear Admiral Walden L. Ainsworth and comprised the US light cruisers Honolulu and St Louis, the New Zealand light cruiser Leander, and the US destroyers Nicholas, O’Bannon, Taylor, Jenkins, Radford, Ralph Talbot, Buchanan, Maury, Woodworth and Gwin.

For battle, these Allied vessels deployed in a single column with five destroyers in the van followed by the light cruisers and then by five destroyers in the rear. Each group of five destroyers formed a squadron. The first of these, designated Destroyer Squadron 21, was commanded by Captain Francis X. McInerney, and the second was Destroyer Squadron 12 commanded by Captain Thomas J. Ryan’s Destroyer Squadron 12. The latter had only recently been assigned to the task force, as had Leander that had been assigned to Ainsworth’s force following the loss of the US Helena in the 'Battle of Kula Gulf' on 6 July. Together, the three cruisers were grouped together as Cruiser Division 9. Ainsworth’s task was to prevent Japanese troops and supplies from landing as part of efforts to stem the flow of reinforcements towards Munda.

TF18 departed its base around Tulagi at 17.00 on 12 July under good conditions characterised by calm water and a clear sky. Passing Savo island, Ainsworth steered a course along the western coast of Santa Isabel island, hoping to use it to hide his force from Japanese reconnaissance aircraft. His plan for the attack was to use the five van destroyers to fire torpedoes while his cruisers manoeuvred into a position to use their main guns. After laying down a heavy barrage the cruisers would then manoeuvre once again to avoid return torpedoes from the Japanese destroyers. Having gone to general quarters as a result of concerns about being spotted in the bright moonlight, at about 00.00 the US task force altered course towards Visu Visu. The Allied ships then increased speed following reports from Allied reconnaissance aircraft that had spotted Isaki’s force about 26 miles (42 km) away. Hamstrung by their slowest ship, Leander, Ainsworth’s task group was able to make only 28 kt, while Isaki’s force was estimated to be cruising at 30 kt.

As the skies began to grow overcast, at 01.00 on 13 July, the Allied ships established radar contact about 20 miles (32 km) to the east of the northern tip of Kolombangara. Ainsworth assumed he had complete surprise as the Japanese lacked radar but, in reality, the Japanese had been aware of the Allied force for almost two hours. Despite not possessing radar, the Japanese ships had the ability to detect the electric impulses of the Allied radar systems, and from this the Japanese crews were able to gain an accurate plot of Ainsworth’s dispositions. After sighting the Japanese force at 01.03, the US destroyers of McInerney’s squadron increased speed to engage the Japanese force with their torpedoes, while the cruisers turned to deploy their main batteries and engage to starboard. Unknown to Ainsworth, the Japanese destroyers had already launched 'Long Lance' heavyweight torpedoes, which had a longer range than the Allied torpedoes. After firing their salvoes between 01.08 and 01.14, the Japanese destroyers turned away to regroup.

The first US torpedoes entered the water about a minute after their Japanese counterparts, with Nicholas engaging Jintsu at a range of just under 10,000 yards (9145 m). Jintsu turned on her searchlight and engaged the Allied ships, but was subjected to concentrated Allied fire from a range of around 9,000 yards (8230 m), with 2,630 rounds fired under the direction of spotting aircraft. After minor corrections to their fall of shot, the Japanese cruiser was heavily damaged. After losing steerage around 01.17, Jintsu came to a dead stop and was eventually reduced to a wreck, broken in two by several torpedo hits, to sink at about 01.45, with the loss of nearly her whole crew including Isaki. On the Allied side, Leander was hit by a shell from Jintsu. The damage was light, but severed radio communications. Several Japanese torpedoes were spotted, and the Allied ships began to take evasive action. These counter-manoeuvres were hampered by faulty communications and thick gunsmoke that reduced visibility. Consequently, several ships turned wide to avoid collisions. One of these was Leander, which was struck by a Japanese torpedo. Severely damaged, the New Zealand cruiser retired from the battle escorted by Radford and Jenkins.

Amid the confusion of the initial engagement, Ryan’s destroyer squadron began its torpedo run from a distance of 7,900 yards (7225 m), firing his first salvo at about 01.12. With the exception of Radford and Jenkins, McInerney’s destroyers were detached from the task force by Ainsworth at 01.31 to pursue contacts to the west following a reconnaissance report from the supporting aircraft that indicated several destroyers were withdrawing in that direction. Meanwhile, the four Japanese destroyer-transports began to withdraw along the coast, while the four Japanese escorting destroyers temporarily retired to the north under the command of Captain Yoshima Shimai to use the cover of a rain squall to reload their torpedo tubes, doing so in only 18 minutes. Ainsworth then pursued the Japanese destroyers with Ryan’s destroyers and his own two cruisers, altering course to the northwest.

Radar contact was re-established by the US ships at 01:56, but there was uncertainty among Ainsworth’s staff about the identity of the ships. Believing that they might be McInerney’s destroyers, the US ships initially held their fire while they sought to confirm the location of three detached destroyers. At 02.03, starshells were fired to illuminate the contacts, which had started to withdraw. Shortly after this, Ainsworth deployed his ships to begin firing with their main batteries, manoeuvring to starboard. In the process, they moved into the path of a number of the torpedoes which had been fired by the Japanese destroyers before they had turned about. In the process, St Louis and Honolulu were each struck by torpedoes and damaged, although this was not mortal. The destroyer Ralph Talbot managed to reply with a salvo of four torpedoes, but these hit nothing. A minute later the destroyer Gwin was also struck by a torpedo amidships, inflicting heavy damage. Despite efforts by her crew to save the ship, Gwin had to be scuttled at 09.30. A total of 61 of Gwin's men were killed as a result of the torpedo attack, and her surviving crewmen were subsequently evacuated on Ralph Talbot.

Following the battle, Ainsworth’s force withdrew to Tulagi. Steaming through 'The Slot' in daylight risked Japanese air attack, and as a result, Ainsworth requested air support and a strong fighter force was provided from bases in the Russell islands to cover the withdrawal. Early on 13 July, a force of 18 Japanese dive-bombers, escorted by 20 fighters, was despatched to attack the Allied ships, but was turned back after clashing off Visu Visu.

Except for Jintsu, which went down with 482 men, the Japanese force escaped damage. After withdrawing along the coast, the four destroyer transports had diverted through the Vella Gulf and landed their 1,200 men at Sandfly Harbour on the western coast of Kolombangara. They completed unloading at 03.40, after which the Japanese ships searched for Jintsu's survivors and then returned to Buin. A total of 21 survivors was subsequently rescued by the Japanese submarine I-180, and a few others were rescued by US ships. Allied losses amounted to one destroyer sunk, and three light cruisers damaged, one of them heavily. A total of 89 Allied sailors was killed, including 28 New Zealanders. Honolulu and St Louis were out of action for several months, while Leander was under repair for a year and did not return to action during World War II.

The Japanese had won a tactical victory, and had again demonstrated that they possessed superior night-fighting techniques. Ainsworth’s force had been unable to prevent the flow of Japanese reinforcements to the south as the lines between Bairoko and the Diamond Narrows remained open. Nevertheless, in strategic terms, the battle forced a change in Japanese tactics. Combined with the earlier 'Battle of Kula Gulf', the engagement eventually deterred the Japanese from future use of the Kula Gulf to reinforce Munda. Admiral Chester W. Nimitz, commander-in-chief of the US Pacific Fleet, also mandated a change in tactics, deciding that the use of cruisers in the confined waters around the Solomon islands group was too dangerous and also ineffective. Meanwhile, their destroyer losses forced the Japanese to use of Daihatsu barges to move reinforcements between the Shortland islands group and the Kula Gulf. Consequently, the US Navy concentrated responsibility for its interdiction efforts on its destroyer and PT-boat forces.

Throughout July and into the early part of August, a series of nightly actions took place involving US destroyers, PT-boats and aircraft against the Japanese reinforcement efforts. The most significant action during this time came on the night of 19/20 July, when a force of 11 ships, consisting of cruisers and destroyers under Rear Admiral Shoji Nishimura, was detected by US aircraft in 'The Slot'. At least one destroyer, Yugure, was sunk, and the heavy cruiser Kumano was damaged, while four US aircraft were lost. After this, the Japanese chose to use the Vella Gulf and the Blackett Strait along the western coast of Kolombangara rather than the direct route through the Kula Gulf. This resulted in the 'Battle of Vella Gulf' and 'Battle off Horaniu' early in August. Late in September and early in October, the Japanese began evacuating their ground troops from Kolombangara. A series of interdiction actions took place during which the US Navy claimed to have sunk 46 barges, killing thousands of Japanese troops. Another action was fought between Japanese and US destroyers off Kolombangara on the night of 2/3 October during which both sides ineffectively exchanged torpedoes and gunfire.