Complex sentence: When the First World War was declared, the airfield became a gathering point for Holderness villagers in the event of an invasion and the East Yorkshire Regiment used the airfield as a parking place for their heavy artillery.
Split into simpler sentences: When the First World War was declared, the airfield became a gathering point for Holderness villagers in the event of an invasion. The East Yorkshire Regiment used the airfield as a parking place for their heavy artillery.