Gabriel Byrne once said of his scene-stealing co-star in this film "never act with children, dogs, or Denholm Elliott!"
The name of the airbase is never mentioned. However at one point Nick views a press clipping which states that the (presumed) hit-and-run driving incident occurred in the village of Brandon. That's in Suffolk, adjacent to the US airbase at RAF Lakenheath. (However, the building Nick is seen parked outside when he asks, and is denied, permission to visit the base commander, is not at Lakenheath, it looks more like RAF Uxbridge which would have been easier to get permission to film at, and is also very close to the Shepperton studio where the film was made.)
The film's title Defense of the Realm (1985) is derived from British legal legislation entitled The Defence of the Realm Act 1914, which is abbreviated as DORA. The long title of the Defence of the Realm Act 1914 reads "An Act to confer on His Majesty in Council power to make Regulations during the present War for the Defence of the Realm." The law was passed by the British Parliament on 8th August 1914, which was four days after the beginning of World War I.
Whilst shooting the opening shot of a car driving over the camera on a deserted road (which involved digging a trench in the road) the car crashed into the camera and crane but the shot was still used.