Complex sentence: U.S. Army doctrine held that tanks did not fight tanks but supported infantry, and the tank destroyers were formed to be used as a counter to massed formations of enemy armored units, acting as independent battalions attached to divisions or Corps.
Split into simpler sentences: U.S. Army doctrine held that tanks did not fight other tanks but supported infantry. The tank destroyers were formed to as a counter force to massed formations of enemy armored units, acting as independent battalions attached to divisions or corps.