As the Allies painstakingly advanced northward through Italy, the 1st Canadian Division took responsibility for the eastern flank of the front. On 6 December, the Canadians crossed the Moro River and, eight days later, seized the vital crossroads at Casa Berardi in furious fighting. The stage was set for the attack on Ortona.
The Seaforth Highlanders and The Loyal Edmonton Regiment were responsible for taking the town, which was defended by some of the best German units in Italy, including the Luftwaffe's elite 1st Paratroop Regiment. The German engineers had systematically demolished some buildings to create clear fields of fire. The rubble provided cover for German machine gun and anti-tank crews, and the remaining buildings housed German defenders on every floor. In order to avoid the murderous German fire that swept every street, The Loyal Edmonton Regiment devised the tactic of "mouse-holing." The troops used small explosive charges or anti-tank guns to blow holes in the walls of adjoining buildings. Grenades and machine gun fire cleared the floor, and the troops then repeated the process. One important departure from the techniques they had learned in the United Kingdom was to enter the adjoining building from the top rather than the bottom floor. The Canadians found that when entering on the bottom floor as they had been taught, the Germans were able to drop grenades from the upper floors. By entering from the top, they were able to drop them on the German defenders below. The Canadians used these tactics to take whole blocks, house by house.
They systematically eliminated every German position and pushed them inexorably back. On 27 November, the beaten German forces withdrew before a flanking movement by the Princess Patricia's Canadian Light Infantry could cut the Germans' line of retreat. The Loyal Edmonton Regiment and Seaforth Highlanders had defeated some of the best German units in Italy.
Throughout the battles that culminated with Ortona, the Canadian presence in Italy was undergoing a major transformation. By reinforcing 1st Infantry Division and the 1st Armoured (previously Tank) Brigade with 5th Canadian Armoured Division, Canada was increasing its contingent to an army corps, 1st Canadian Corps. In addition to the 15,000 troops of the armoured division, the contingent included the 8,500-strong Canadian Corps troops (the Headquarters and units of the supporting arms and services--engineers, anti-aircraft artillery, transport, supply, medical, etc) and some 3,700 army troops (medium artillery being the biggest component). These troops had to be transported from England to the Mediterranean, equipped from theatre resources, and then make their way up the boot of Italy to the front. Headquarters 1st Canadian Corps was activated in January. The Armoured Division's 11th Infantry Brigade was active in the Ortona salient by early January 1944, giving respite to the decimated battalions of the 1st Division. The division's other component, the 5th Armoured Brigade, had difficulty acquiring tanks and was not in action until May during the Liri Valley battles that were part of the operations to break through the Hitler Line.