Complex sentence: S Stock sub-surface trains, delivered by Bombardier Transportation in Derby to the London Underground, are replacing 177 trains on the Metropolitan, District, Hammersmith & City, and Circle lines with a standardised fleet of 191 trains (1,395 cars).
Split into simpler sentences: S Stock sub-surface trains, delivered by Bombardier Transportation in Derby to the London Underground, are in the process replacing 177 trains on the Metropolitan, District, Hammersmith & City, and Circle lines. The order consists of a standardised fleet of 191 trains (1,395 cars).