Despite US forces being subjected to a major armored thrust by the Germans in the Ardennes, Tank Destroyer units were not ordered to engage the enemy according to stated doctrine. This was because most units had already been attached to Divisions and had been broken up into smaller infantry support units in a similar fashion to the way separate Tank Battalions had been. Moreover, the loss of lines of communications led to the smaller units being controlled by local commanders rather than being directed by Corps or Army commanders.