Military attaché
In 1935 he returned to Germany as a member of the International Force supervising the Saarland plebiscite. Afterwards, he joined the German Intelligence Section at the War Office. In 1937 he became Assistant Military attaché in Berlin to Noel Mason-Macfarlane. As such, Strong got to know many senior German military officers personally, including Wilhelm Keitel. Like Mason-Macfarlane, he became convinced that war with Germany was imminent and inevitable.