Complex sentence: After the outbreak of World War Two, Blake's first significant command, as a Major General, was Officer Commanding 7th Military District, based in Darwin, from 1941 gained unexpected importance when war with Japan broke out.
Split into simpler sentences: After the outbreak of World War Two, Blake's first significant command, as a Major General, was Officer Commanding, 7th Military District, based in Darwin, from 1941. The post gained unexpected importance when war with Japan broke out.