In January 1944 Mayne was promoted to lieutenant colonel and appointed commanding officer of the re-formed 1st SAS Regiment. He subsequently led the SAS with great distinction through the final campaigns of the war in France, the Netherlands, Belgium, Germany and Norway, often campaigning alongside local resistance fighters including the French Maquis. In recognition of his leadership and personal disregard for danger while in France, in which he trained and worked closely with the French Resistance, Mayne received the second Bar to his DSO. The official citation stated: