Harold Charrington's 1st Armoured Brigade was to cover the withdrawal of Savige Force to Larissa and thereafter the withdrawal of the 6th Division under whose command it would come; overseeing the withdrawal of Allen Force which was to move along the same route as the New Zealand Division. The British, Australian and New Zealand forces remained under attack throughout the withdrawal. On the morning of 18 April, the Battle of Tempe Gorge, the struggle for the Pineios Gorge, was over when German armoured infantry crossed the river on floats and 6th Mountain Division troops worked their way around the New Zealand battalion, which was subsequently dispersed. On 19 April, the first XVIII Mountain Corps troops entered Larissa and took possession of the airfield, where the British had left their supply dump intact. The seizure of ten truckloads of rations and fuel enabled the spearhead units to continue without ceasing. The port of Volos, at which the British had re-embarked numerous units during the prior few days, fell on 21 April; there, the Germans captured large quantities of valuable diesel and crude oil. Withdrawal and surrender of the Greek Epirus Army As the invading Germans advanced deep into Greek territory, the Epirus Army Section of the Greek army operating in Albania was reluctant to retreat. By the middle of March, especially after the Tepelene offensive, the Greek army had suffered, according to British estimates, 5,000 casualties, and it was fast approaching the end of its logistical tether. General Wilson described this unwillingness to retreat as "the fetishistic doctrine that not a yard of ground should be yielded to the Italians." Churchill also criticized the Greek Army commanders for ignoring British advice to abandon Albania and avoid encirclement. Lieutenant-General Georg Stumme's XL Corps captured the Florina-Vevi Pass on 11 April, but unseasonal snowy weather then halted his advance. On 12 April, he resumed the advance, but spent the whole day fighting Brigadier Charrington's 1st Armoured Brigade at Proastion. It was not until 13 April that the first Greek elements began to withdraw toward the Pindus mountains. The Allies' retreat to Thermopylae uncovered a route across the Pindus mountains by which the Germans might flank the Hellenic army in a rearguard action. An elite SS formation—the Leibstandarte SS Adolf Hitler brigade—was assigned the mission of cutting off the Greek Epirus Army's line of retreat from Albania by driving westward to the Metsovon pass