Complex sentence: Vian returned to the UK shortly before World War II broke out, an appointment to command the boys' training establishment, HMS "Ganges" was cancelled, and he was appointed to command of the 11th Destroyer Flotilla.
Split into simpler sentences: Vian returned to the UK shortly before World War II broke out. An appointment to command the boys' training establishment HMS "Ganges" was cancelled, and he was appointed to command of the 11th Destroyer Flotilla.