Complex sentence: Its final revenue run came on June 14,1958, when 765 was activated to supply steam heat to a stranded passenger train that December, it became the last Nickel Plate Road Berkshire under steam.
Split into simpler sentences: Its final revenue run came on June 14,1958. When it was activated to supply steam heat to a stranded passenger train that December, it became the last Nickel Plate Road Berkshire under steam.