In May 1940 while "Isis" was in dock for repairs, Clouston was attached the Naval Shore Party of eight officers and 160 men under the command of Captain William Tennant sent to the port of Dunkirk to help organise the evacuation. The Naval Shore Party embarked on the destroyer at Dover and sailed on 27 May. Three officers cut cards for their assignments. Clouston won the eastern mole, a narrow wooden walkway mounted on a concrete breakwater, not designed to be used by ships, but the only part of the port that had not been heavily bombed by the "Luftwaffe". For the next five days, Clouston organised and regulated the flow of men along the mole into the waiting ships.