'Sperraufgaben' was a German undertaking ordered by Generaloberst Alexander Löhr, the Oberbefehlshaber 'Südost', to reconnoitre and prepare fall-back positions for the formations of his Heeresgruppe 'E' in the hill region to the south-west of Kalambaka and north of the road linking Trikala and Larissa in German-occupied Greece (23 November 1943).