Complex sentence: During his posting on "Javelin", a mutiny broke out whilst Leach was the Duty Officer: he "conducted himself well under difficult circumstances" and after the mutiny was put down the captain and first lieutenant were re-appointed.
Split into simpler sentences: During his posting on "Javelin", a mutiny broke out whilst Leach was the Duty Officer. He "conducted himself well under difficult circumstances" and after the mutiny was put down the captain and first lieutenant were re-appointed.