Complex sentence: It was often referred to as "the Slow and Dirty", or sometimes "the Slow and Doubtful", but it always commanded a considerable loyalty from railway enthusiasts, and when it closed in 1966 it was widely mourned.
Split into simpler sentences: It was often referred to as "the Slow and Dirty" or sometimes "the Slow and Doubtful". It always commanded a considerable loyalty from railway enthusiasts, and when it closed in 1966 it was widely mourned.