 Complete the following phrase:  When the German offensive in the west opened on 10 May, 12 AA Bde was not involved in the BEFs advance into Belgium and subsequent retreat after the German Army broke through the Ardennes. However, the AASF flew many missions and took heavy casualties against the Ardennes breakthrough, while its airfields were subjected to dive-bombing and low-level attacks with which the old 3-inch guns and their Vickers Predictor No 1 and height-finders could not cope. At Condé Vraux the Luftwaffe destroyed six of 114 Squadrons Blenheims and damaged the remaining 12, as well as the airfield and petrol dump, putting the whole squadron and airfield out of service at the beginning of the battle, although the ground defences accounted for over half the attacking aircraft. By late May the BEF was cut off and was being 