On 8 April 1941, the German 6th Mountain Division cracked the Metaxas Line in the most unlikely of places: the extremely mountainous far west of the line, after scaling the twin heights of Demir Kapou and Kale Bair. Both mountains were over 7000 ft (twice the height of Riva Ridge) and thought by the Greeks to be insurmountable. Nonetheless, the feat was almost in vain as just west, the 2nd Panzer Division blew through Yugoslavia and raced near unopposed toward Thessalonica. To the northwest, the advanced guard of the 1st SS Leibstandarte Adolf Hitler Brigade, Hitler’s elite bodyguard, entered the northern end of the Monastir Pass, whose southern exit outflanked Gen Maitland Wilson’s Force W along the Halciamon Line.
Wilson knew of the German advances in near real time due to Ultra intelligence intercepts but couldn’t convince the Greeks to retreat. He couldn’t compromise the nature of his information, and in any case the Greeks were experiencing great success on the eastern end of the Metaxas Line, and were unwilling to disengage from a “winning” battle. Wilson dispatched an Australian brigade group to the southern end of the Monastir Gap, but even by force marching they barely made it there in time. Wilson essentially sacrificed them to save the rest of Force W. Wilson was only able to stay ahead of the Germans due to his Ultra intelligence. Force W, and any Greeks nearby, retreated first to the Mt Olympus Line, and then to the Thermopylae Line further south. But both would be outflanked, and two more brigades, Kiwis these times, would be sacrificed to slow down the advance so the rest of Force W could evacuate to Crete.