In March 1942 in Scotland, Tui and the four Isles class trawlers, Killegray, Inchkeith, Sanda and Scarba had been newly build for New Zealand. They were formed into a flotilla and departed from the River Clyde with a convey bound for Canada. The trawler flotilla then left for Auckland, arriving there in August.
In Auckland Tui was assigned to the 25th Minesweeping Flotilla and sailed for Suva to replace Matai. In December she joined her sister ships Kiwi and Moa at Noumea. The 25th Minesweeping Flotilla had been offered to COMSOPAC, and by early December Tui, Moa, and Kiwi with Matai as flotilla leader, were all together at Noumea ready to move north. They sailed for the Solomons, escorting a convey some of the way. Making Tulagi their base they began anti-submarine screen patrols on 19 December 1942 off Tulagi and Lunga Point, Guadual Canal.
On 21 January 1943, Tui and Moa came across four Japanese landing barges stopped close inshore. When Tui and Moa closed in, those aboard the barges opened fire with machine guns and small arms, and got underway. At close range Moa fired on the leading barge, but a fluke shot passed through the 4-inch gun aperture, ignited a cordite charge and injured all seven in the gun crew. Moa managed to silence the first barge and sink the last in line with 20mm fire, then withdrew and attended to the cordite fire and injuries. Tui then opened fire on the barges, sinking one with her 4 inch gun, and the remaining two escaped inshore in the darkness.
On 19 August 1943, while escorting a convey from Noumea, Tui picked up a submarine contact. She made an initial run over it without using depth charges, a second run dropping two depth charges, and a third run throwing another two depth charges. Contact was lost and Tui signaled some US seaplanes who joined the search. A plane indicated that Tui should investigate smoke on the horizon. The submarine was sighted on the surface and Tui opened fire at maximum range, scoring one and possibly two hits. Aircraft then dropped depth charges and the submarine sank. She was the Japanesse Submarine I-17, 2,190 tons, 108m long, built in 1939. Ninety-seven crewmen were lost. Tui picked up six survivors who said that Tui's depth charge attacks had damaged the submarine and forced it to the surface.