 In 1939, the 20th Battalion merged with the 19th Battalion to become the 20th/19th Battalion, adopting the territorial designation of the "Parramatta and Blue Mountains Regiment".Following the outbreak of World War II, the 20th/19th Battalion was transferred from Sydney to Darwin in the Northern Territory, where they were to form part of the town's garrison.These two battalions were delinked on 1 November 1941 as part of the expansion of the Australian military following Japan's entry into the war.