In July 1944, the 25th Battalion deployed to New Guinea where they were based around Madang until November when the battalion was transferred to Bougainville Island, landing at Torokina, where the Australians had taken over from the American force that had previously been fighting a campaign against the Japanese on the island. The Australians then began a three-pronged offensive in the northern, central and southern sectors of the island to clear the Japanese from the island. As part of this offensive, the 25th Battalion initially took part in the fighting in the central sector, and in late December fought in the Battle of Pearl Ridge before joining the southern drive on the Japanese stronghold of Buin in early 1945. By March they had crossed the Puriata River and begun moving inland towards a position that became known as "Slater's Knoll".