Complex sentence: With a crew complement of 86, Enterprise was Starfleet's first long-range exploration vessel with a theoretical top speed of warp 5.2 by the fourth to last episode of the 4th season, considerably faster than any other human vessels of the era.
Split into simpler sentences: With a crew complement of 86, Enterprise was Starfleet's first long-range exploration vessel. The "Enterprise" had a theoretical top speed of warp 5.2 by the fourth to last episode of the 4th season, considerably faster than any other human vessels of the era.