US Tank Destroyer doctrine called for mobile units to quickly move to a given position, fire upon enemy armor once they were within range, and then to retreat quickly and take up another position when endangered by enemy fire. Design specifications were thus geared towards speed and mobility, turreted armament capable of defeating enemy armor, and only enough armor to resist small arms fire. This was in contrast to the slower Russian and German tank destroyers, which were heavy armed and armored and were built without turrets.