At the outbreak of the first World War, de Wet returned to service; he was mentioned in despatches and awarded the CBE for valuable services as Divisional Naval Transport Officer in Vancouver. Continuing in service, he was subsequently Principal Naval Transport Officer during the evacuation of Constantinople in 1923, Principal Sea Transport Officer in North China in 1927 and Officer in Charge of Sea Transport in Egypt between 1924 and 1926 and again between 1928 and 1933.