After being mobilised for war service on 15 December 1941, the regiment was moved to Sydney, entraining at Oakbank on 25 December 1941. Embarking on the transport "Aquitania" at Woolloomooloo two days later, the regiment sailed for New Guinea. Initially they were used in the garrison role, but after the Japanese landed in New Guinea, the regiment became involved in the fighting. During the Battle of Buna–Gona which took place in late 1942 and early 1943, the regiment deployed a troop of four guns under command of Captain N.R. Stokes. These were QF 4.5-inch howitzers. Two of these guns were flown to Dobodura on 20 December. Two were transported by sea and landed at Hariko on 23 December. The troop was initially positioned on the Dobodura–Buna track. This was about 2,500 yards (2,200 m) south of the bridge between the two strips. The troop fired in support of the US 32nd Division during fighting at Buna. The troop later moved to a position near Giropa Point to support the Allied attacks to take the final Japanese positions at Sanananda and Giruwa.