Complex sentence: In 1918, the Royal Air Force began using the field behind the range for experimental mail flights, and the airport opened officially in 1920 as the "Ottawa Air Station", one of the six original airfields opened across Canada by the new Air Board.
Split into simpler sentences: In 1918, the Royal Air Force began using the field behind the range for experimental mail flights. The airport opened later in 1920 as the "Ottawa Air Station", as one of the six original airfields opened across Canada by the new Air Board.