When the Germans turned the flank at Aliakmon

After the German attack on Yugoslavia and Greece in early April 1941, the Germans quickly crossed into the "upper Aliakmon valley". This flanked the Greeks facing Albania and also W Force. The British had no choice but fall back on Thermopylae. That meant withdrawing across Thessaly, a plain. That also meant that the main airfields would be lost to the advancing Germans. With the Greek government at the breaking point, the commanders decided to stage a complete withdrawal of British forces. For all the sacrifices made to send troops to Greece, it all came to nought. British forces were unable to affect the outcome in the Balkans and almost lost North Africa, as well. This is based on the account in Vol.II of the Official History.