The numerous postponements of the German 1940 offensive in the west were, for the most part, the result of Hitler's injunction that the attack be made in good flying weather.
 The older military history of the Ardennes is narrated on a somewhat antiquarian basis in Revue Historique de l'Armee, 1955, IIe Annee, Numero 2. For the 1940 campaign see L. Menu, Lumiere Sur Les Ruines, Paris, 1953; also M. Fouillien and J. Bouhon, Mai 1940: La Bataille de Belgique, Bruxells, n.d.
 The best of numerous terrain descriptions of the Ardennes was prepared by the German General Staff in 1940, especially for the offensive in the west. It is entitled Militaergeographischer ueberblick ueber Belgien und angrenzende Gebiete. See also the British official publication of 1918: A Manual of Belgium and the Adjoining Territories (ed. The Admiralty). The best analysis of German military thought on the problem presented by the Ardennes terrain is in a manuscript by Magna E. Bauer entitled Comparison Between the Planning for the German Ardennes Offensive in 1944 and for the Campaign in the West in 1940 (1951). OCMH.