Some twenty-five divisions would be pulled from quiet sectors of the western front, the quieter sectors of the eastern front, and OKW's (that's Oberkommando der Wehrmacht, the Supreme Command of the Armed Forces, for the uninitiated) strategic reserve, and would drive from the Siegfried Line between the town of Diekirch along the Our River in the south and Malmédy and Monschau in the north. In keeping with plans that received Hitler's personal support, it was bold to the point of delusion. The genesis of Unternehmen Wacht am Rhein came in autumn of 1944, shortly after British forces liberated Antwerp and during Montgomery's ill-fated airborne attack on Arnhem. To start there, however, would be to tell the middle of the story before the beginning, and I don't truck with clever literary devices like that.
