Complex sentence: In 2008, Chiltern ordered four 2-car "Turbostar" units to increase capacity, and these were delivered to Chiltern in May 2011, entering passenger service on 8 June 2011.
Split into simpler sentences: In 2008, Chiltern ordered four 2-car "Turbostar" units to increase capacity. These were delivered to Chiltern in May 2011, entering passenger service on 8 June 2011.