Her service in World War II started in the Dutch East Indies, where she engaged the enemy off Makassar on 8 February 1942. "Haguro" then played a key role in the Battle of the Java Sea on 27 February 1942, first sinking the destroyer and then later the same day the Allied fleet's flagship, the cruiser ; both by torpedo. Two days later, on 1 March 1942 in another action south of Borneo, "Haguro" took part in the sinking of the cruiser and the destroyer .