 In December 1944 , Strong identified a large German reserve . The Germans devised an elaborate deception plan , and because the troops were being assembled inside Germany , they relied on secure phone and teleprinter lines rather than radio . Ultra and signal intelligence therefore dried up . Ultra detected German hoarding of fuel , but this was misinterpreted as a response to a critical shortage rather than building up a reserve . However , the withdrawal of armoured units from the front line was duly noted , and by 20 November , using agents , aircraft and prisoner interrogations , SHAEF had located and enumerated the divisions of the Fifth Panzer Army east of Aachen and the Sixth Panzer Army east of the Roer River . Strong informed Smith that the German armoured reserves might be sent to the Eastern Front , or used for a counterattack against an Allied penetration of the front , but might also be used for a counterattack during a period of bad weather . In early December , SHAEF detected tank movements in the Bitburg area , and Strong became worried about a possible counterattack against the Allied lines in the Ardennes or the Vosges . Smith sent Strong to warn Lieutenant General Omar Bradley , the commander of the 12th Army Group , of the danger . Bradley 's response was succinct : " Let them come . " 
