"before morning they would land at the big airfield in Wiltshire"
Creative Commons AttributionWiltshire - Credit: Phillip Capper

Wiltshire is one of the larger counties in southern England. It takes its name from the town of Wilton on the river Wylye. The administrative center is Salisbury.

Wiltshire is home to numerous British military units, including army regiments stationed around Salisbury Plain.  The airfield in question is likely to be one of the big Royal Air Force bases, such as Boscombe Down or Lyneham.