Britain's biggest mimic air war, the Home Defence Air Exercises, which has 'broken out'in an area extending from the Thames Estuary to the mouth of the Humber. Aircraft from 54 Squadron, based at RAF Northolt, Essex and ground defence units are engaged in the manoeuvres, the Home Defence Air Exercises. Photo shows, members of the 32nd Battalion Royal Engineers (Territorials) at their crosstown locator. 5 August 1938