Complex sentence: When the First World War broke out he attempted to join the Indian army but only served briefly in the Bombay volunteer rifles and as an intelligence officer in the defence of Bombay port between 1915 and 1919.
Split into simpler sentences: When the First World War broke out, he attempted to join the Indian army. He served briefly in the Bombay volunteer rifles and as an intelligence officer in the defence of Bombay port between 1915 and 1919.