Complex sentence: During World War II when Bankstown Airport became a key air force base in the war effort the specially constructed bunker became an important Royal Australian Air Force headquarters from 1945 until its closure in 1947.
Split into simpler sentences: During World War II, Bankstown Airport became a key air base in the war effort. The specially constructed bunker became an important Royal Australian Air Force headquarters from 1945 until its closure in 1947.