Complex sentence: During the Second World War the occupancy of the hospital rose significantly from 3,165 to 12,136 as it treated civilian and military casualties and many local businesses and university buildings were converted into extra wards.
Split into simpler sentences: During the Second World War the occupancy of the hospital rose significantly as it treated civilian and military casualties. Bed occupancy rose from 3,165 to 12,136, with many local businesses and university buildings being converted into extra wards.