He wrote that the German offensive was complicated and at times chaotic, rather than a simple armoured rush through the Ardennes and across France. French strategy had left the Allies vulnerable to a breakthrough along the Ardennes and the army failed adequately to react to the breakthrough and the massing of tanks; tactically the German tanks and infantry had defeated French defences that were rarely formidable. French military intelligence also failed to identify the main German attack and even on the morning of 13 May, thought that the Schwerpunkt (main effort) was in central Belgium.