Complex sentence: Owen, disappointed with the lack of interest in his firearm, enlisted in the Second Australian Imperial Force (AIF) in May 1940, joining the 2nd/17th Battalion, Royal New South Wales Regiment.
Split into simpler sentences: Owen, disappointed with the lack of interest in his firearm, enlisted in the Second Australian Imperial Force (AIF) in May 1940. He was assigned to the 2nd/17th Battalion, Royal New South Wales Regiment.