 In 1939, these two battalions were delinked, however, the 19th was further amalgamated with the 20th Battalion to form the 20th/19th Battalion, adopting the territorial designation of the "Parramatta and Blue Mountains Regiment".At the start of World War II, the 20th/19th Battalion served as a machine-gun unit in Sydney before part of it was sent to Darwin to serve as a garrison force in 1941.The machine gunners later formed part of the 6th Machine Gun Battalion.