Complex sentence: During the Second World War, he served as a Lieutenant commander in the Royal Naval Reserve for two and a half years and was then a purser with the P&O Line before joining the staff of the BBC in 1945.
Split into simpler sentences: During the Second World War, he served for two and a half years as a Lieutenant-Commander in the Royal Naval Reserve. He then became a purser for the P&O Line before joining the staff of the BBC in 1945.