US tank destroyer doctrine was essentially a defensive and reactive measure. They existed to slow down, or even stop, a Blitzkrieg style armored thrust and prevent it from penetrating too deeply or from encircling friendly forces in a pincer movement. The idea was that, once an enemy armored thrust was expected to break through, the tank destroyer battalion (as a single unit and operating behind the front lines), would position itself to intercept the enemy while a more complete defense is organized at corps or higher level. This was to be the case for both towed and mobile tank destroyer battalions. As the enemy armored thrust approached, organic reconnaissance units would communicate to battalion commanders the best locations for tank destroyer units to place themselves in, while organic pioneer units would create blockades or help the tank destroyers dig into their positions. As the enemy armored thrust came within range, the hidden tank destroyer units would fire upon enemy tanks and then retreat to another position once they began to draw fire.