 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 George Stumme's Fortieth 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 and from there to Ioannina. On 13 April, attack aircraft from 21, 23 and 33 Squadrons from the Hellenic Air Force (RHAF), attacked Italian positions in Albania. That same day, heavy fighting took place at Kleisoura pass, where the Greek 20th Division covering the Greek withdrawal, fought in a determined manner, delaying Stumme's advance practically a whole day. The withdrawal extended across the entire Albanian front, with the Italians in hesitant pursuit. On 15 April, Regia Aeronautica fighters attacked the (RHAF) base at Paramythia, 30 miles south of Greece's border with Albania, destroying or putting out of action 17 VVKJ aircraft that had recently arrived from Yugoslavia.
