Complex sentence: The defence of Karachi harbour was therefore paramount to the Pakistani High Command and it was heavily defended against any air or naval strikes, including cover from strike aircraft based at two airfields in the area.
Split into simpler sentences: The defence of Karachi harbour was therefore paramount to the Pakistani High Command and it was heavily defended against any air or naval strikes. Karachi received the best defence Pakistan had to offer, including cover from strike aircraft based at two airfields in the area.