Wilkinson transferred to the Royal Artillery on 1 June 1942, and was again a temporary lieutenant-colonel, commanding 99th Light Anti-Aircraft Regiment, when on 13 May 1944, during the final stages of the Battle of Monte Cassino he performed the actions that led to his appointment as a Companion of the Distinguished Service Order on 21 September 1944. His regiment had been detailed to make smoke to cover the bridges over the Gari River, early in the day it was reported that there was no smoke covering one particular bridge (codenamed Amazon). Wilkinson took a jeep to investigate the situation for himself, approaching the bridge the trailer from another jeep was found, which contained the equipment for making smoke, which was then loaded into his own jeep. It was later determined that both officers responsible for the bridge had been injured (one killed), and the sergeant had also been killed, and initial supplies of smoke canisters had been exhausted. Wilkinson proceeded to cross the bridge on foot, under mortar and small arms fire, carrying replacement smoke canisters. He managed to begin the re-establishment of the smoke screen, left the one man still there tending the new smoke canisters, and gathered an additional party of men to ensure the screen was maintained.