Complex sentence: Hordern received a commission into the Royal Navy and went on to serve on HMS "Illustrious" in Operation Ironclad in 1942, and later as a Lieutenant-Commander in the office of the First Sea Lord.
Split into simpler sentences: Hordern received a commission into the Royal Navy and went on to serve on HMS "Illustrious", taking part in Operation Ironclad in 1942. He also held a post with the rank of Lieutenant-Commander in the office of the First Sea Lord.