Ashigara was transporting Japanese troops from the Dutch East Indies for the defence of Singapore and its loss caused many casualties.

The voyage of Ashigara was revealed to the Allies by Ultra decrypts, which enabled Rear-Admiral James Fife, the US commander of submarines, South-West Pacific, to lay an ambush.

Trenchant fired a long-range salvo of eight torpedoes at Ashigara, from a tactically-awkward angle but the Japanese cruiser was too close to the Sumatran shore to turn away.

[2] In early 1945 the Japanese began to remove distant garrisons in the South-West Pacific to reduce the defence perimeter to the Celebes, Borneo, Java, Sumatra and hold it for as long as possible, with Indo-China and Malaya in the centre of the defensive zone.

11 to bring Japanese army troops from the Lesser Sunda Islands to Singapore via Batavia (now Jakarta) continued in June 1945.

[7][a] No air cover was forthcoming as the Japanese Army considered the moves a purely naval matter but reconnaissance flights of the Bangka Strait were flown from bases in western Java.

[1] In June, Ultra decrypts of Japanese naval messages revealed that Ashigara and Kamikaze were to move troops of the 48th Division from Jakarta to Singapore.

With some reluctance, Fife allowed Trenchant into the Bangka Strait, despite its dangerous shoals, currents and the presence of an Allied minefield.

It soon became clear to Hezlet that he could not reach a firing position closer to Ashigara than 4,000 yd (2.0 nmi; 2.3 mi; 3.7 km), almost at the maximum range of his torpedoes.

[12] Kamikaze had returned to the area and dropped three patterns of depth charges but these were no closer than 3 mi (2.6 nmi; 4.8 km) from Trenchant.

[14] Japanese losses in the sinking severe, out of 1,600 troops, only 400 were rescued along with 850 of her crew, including Captain Miura and Vice-Admiral Hashimoto, the commander of the 5th Cruiser Squadron.

[13] Ashigara had been the last big Japanese warship in the area, after the cruiser Haguro was sunk during the Battle of the Malacca Strait a month earlier, by British destroyers.