Complex sentence: In the pre-preservation era, the Royal Train had frequently been hauled by steam, one instance being Southern Railway Merchant Navy class 35027'Port Line', which hauled the Royal Train to Windsor and Eton from Hamworthy.
Split into simpler sentences: In the pre-preservation era, the Royal Train had been hauled frequently, one example was of Southern Railway Merchant Navy class 35027'Port Line'. It hauled the Royal Train to Windsor and Eton from Hamworthy.