Promoted to Lieutenant Colonel, Rowley commanded the Stormont, Dundas and Glengarry Highlanders, during the Allied campaign in North West Europe during 1944. The SD&G formed part of 3rd Canadian Infantry Division, whose participation secured the liberation of the Channel ports of Boulogne and Calais. The Canadians launched their attack on Boulogne on 17 September 1944. The battle raged for six days until the remaining German prisoners surrendered on 22 September. Rowley's DSO citation praised his speed and daring after the heavy bombing of the château outside the town, as well as his action under heavy artillery and machine-gun fire as the battalion attacked the citadel: ""This officer's leadership, dash, bravery and unlimited energy were an inspiration to his officers and men, and his action was one of the principal factors in the capture of Boulogne.""