After the abrupt termination of his M-O diary, Denis's military career continued, although in very different directions, and his political thinking evolved away from sympathy with Communist positions. In June 1944, in response to one of M-O's Directive questions that month, he indicated that he was still politically engaged and enjoyed ‘occasional political argument, though it's now a full year since I ceased to be under the direct influence of a keen 100% Marxist, a CP member who would possibly have eventually had me whole-heartedly arguing with him’. He also ceased to be a conscientious objector. While he continued to appreciate many conscientious objectors individually – though not the ‘complete do nothings like Jehovah Witnesses’ (he saw them as priggish and intolerant) – he had turned away from their ‘blindness to the menace of Nazism’ (Directive Response, January 1943).

Denis left Bedfordshire in October 1942 and began combat training, initially in Bury St Edmunds. His Luton bomb-disposal section was later disbanded, and some of its members (still ‘conchies’) became paratroopers and were dropped in France on D-Day with the Royal Army Medical Corps. In late 1942 Denis transferred to the Royal Army Signals Corps, and in a Directive Response to M-O in February 1943, replying to a request for a detailed report on his activities on 10 February, he reported that he had spent the day with a party of a dozen men temporarily situated in the Unitarian Church Hall in Huddersfield, Yorkshire, undergoing signals training. His training continued for months, mostly or entirely in the North, with Denis and his fellow trainees expecting to become part of the widely anticipated European invasion force – what later became known as D-Day. However, the reality, for Denis, would be different: he was posted to India in late 1944, as part of the Air Formation Signals, and then Burma, where he spent the remainder of the war. There he came to know and appreciate Asian peoples, particularly the Indians with whom he came in contact; he continued to exercise what one commanding officer described as his ‘fluent pen’ by writing frequently for the unit magazine; he acted as unit librarian in addition to his other duties, notably managing the post; and he shared his love of music on a Forces wireless programme. Officers wrote of him during the war as ‘an intelligent’ or even a ‘very intelligent man’.