 With the expansion of the Australian force to two Battalion Groups in June 1966, the remainder of the Regiment, less 101st Field Battery, deployed to Vietnam accompanied by 103rd Field Battery, under the command of Lieutenant Colonel Richmond Cubis.In addition, six 155 mm M109 self-propelled howitzers from A Battery, US 2/35th Artillery Battalion were permanently attached at Nui Dat.On 18 August 1966, the Regiment took part in the Battle of Long Tan in support of D Company, 6 RAR, firing 3,198 rounds from their L5s in three hours of battle with the artillery proving critical in ensuring the survival of the infantry.