day - the idea being that a slowing down of the advance was as good as stopping them outright, since the Germans were limited by time. The mobile defense he used at St. Vith involved the use of M36 tank destroyers acting as a base of fire to resist the oncoming German armored thrust, slowing them down enough to then counter-attack them with a force of M4 Sherman tanks. Artillery and Infantry were involved in this process as a combined arms force. The key was not to engage the Germans in a pitched battle, but to slow their advance enough to ruin their offensive timetable. The counter-attacks ensured that the German forces could not break through the slowly retreating forces. Clarke's success was one of the first times armor had been used in a mobile defense. See also Counter-offensive Cult of the offensive Battleplan (documentary TV series) Notes and references Further reading Military tactics Military terminology