German tactics for the offensive involved an initial intense artillery barrage, followed by an immediate infantry attacks by the "volksgrenadier" divisions supported with light assault guns such as the Sturmgeschütz IV. This initial attack with relatively non-mobile and more expendable troops were used to clear major roads for use by the SS panzer divisions, which would then rapidly move to capture bridges on the Meuse river for the final drive to Antwerp. These armored divisions were employed in a much more organized and controlled fashion, and with better leadership, than was usual for the Americans. The German concept of the armored division was an independent unit that carried with it all its supporting elements, making it more mobile and flexible than an American armored division, and able to concentrate greater force at the point of attack. Shock and high speed were intended to overwhelm resistance, as it did during the first drive from the Ardennes in 1940. These tactics made up what was referred to as "blitzkrieg", or lightning war. The German command expected that the allied high command would take weeks to adjust to the impact. But Hitler failed to consider the constricted, winding, often unpaved roads of the northern Ardennes and underrated the capabilities of the American units on the northern shoulder.