In response to the Nazi–Soviet pact on 23 August 1939, the RAF mobilised. Cunningham had been test-flying the de Havilland Dragon airliner. Only 16 were completed before the declaration of war in September. The growing tension in Europe made war more likely. Cunningham was forced to commit himself either to de Havilland or the RAF at this juncture. The RAF had trained him and he felt he could be of far more use in the RAF than test-flying aircraft.