Within days of the declaration of war he reported to an army recruiting centre with the intention of joining a cavalry regiment, but like many others keen to serve he had to wait, and it was not until July 1940 that he started his training. After attending the Royal Military College, Sandhurst, he was commissioned on 1 February 1941 into the 2nd Derbyshire Yeomanry at Ripon. He was posted to the Middle East in July 1941 and transferred to the Nottinghamshire (Sherwood Rangers) Yeomanry. Posted initially at Cairo and Palestine, he found himself stuck at headquarters twenty miles behind El Alamein as a camouflage officer as the Second Battle of El Alamein began. At dawn on 24 October 1942, the Regiment advanced, and suffered numerous casualties from enemy anti-tank guns. Chafing at inactivity, Douglas took off against orders on 27 October, drove to the Regimental HQ in a truck, and reported to the C.O., Colonel E. O. Kellett, lying that he had been instructed to go to the front (luckily this escapade did not land him in serious trouble; in a reprise of 1935, Douglas got off with an apology). Desperately needing officer replacements, the Colonel posted him to A Squadron, and gave him the opportunity to take part as a fighting tanker in the Eighth Army's victorious sweep through North Africa, vividly recounted in his memoir Alamein to Zem Zem, which was illustrated with his own drawings.