Complex sentence: The R17 was a New York City Subway car built in 1955 as one of three car classes purchased in the mid- 1950s, intended to replace many of the pre-World War II IRT cars.
Split into simpler sentences: The R17 was a New York City Subway car built in 1955. One of three car classes purchased in the mid- 1950s, intended to replace many of the pre-World War II IRT cars.