Service chiefs prepare for nine-day air exercise. High-ranking officers of the three Services attended a press conference held at the Headquarters of Bomber Command , Bentley Priory , Stanmore , Middlesex in connection with the nine-days Air Defence exercise which begins on 25th June 1949 . The exercise will be known as Exercise "Foil " and is designed to test out Britain's air defences against ' raids ' made by day and night . Left to right - Air Marshall Sir Aubrey Ellwood KCB , DSO , AOC-inC Bomber Command , Lieut-General Sir G Ivor Thomas , KBE , CB , DSO , MC , GOC-in-C Anti-Aircraft Command and Air Marshal Sir Basil Embry KBE , CB , DSO , DFC , AFC , AOC-inC RAF Fighter Command . 24th June 1949