Complex sentence: Having unsuccessfully attempted to establish a film company between the wars, Ridley rejoined the army in 1939 with the rank of Major and again saw active service with the British Expeditionary Force in France during the Second World War, but was discharged on health grounds.
Split into simpler sentences: Having unsuccessfully attempted to establish a film company between the wars, Ridley rejoined the army in 1939 with the rank of Major. He again saw active service with the British Expeditionary Force in France during the Second World War, but was discharged on health grounds.