 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 . 
