Battle of Dunkirk
Appointed a Companion of the Order of the Bath in the 1939 New Year Honours, Mason-MacFarlane was Director of Military Intelligence with the British Expeditionary Force (BEF) in 1939–40 and during the Battle of Dunkirk was operational commander of "Mac Force," an improvised formation covering the British right flank. For his services, he was awarded the Distinguished Service Order.