 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."
