Bellenger remained in the army's emergency reserve, and when the Second World War broke out in 1939 he was automatically recalled to service. He was commissioned as a captain in the Royal Artillery in February 1940. He went to France as a staff officer in April of that year as part of the British Expeditionary Force. He returned to the United Kingdom briefly in May to take part in the Norway Debate in the Commons that led to the fall of Neville Chamberlain's government. Evacuated from France in June 1940, two months later he resigned his commission. Apart from his parliamentary activities, Bellenger wrote a column for the "Sunday Pictorial" under the byline "Voice of the Services".