The United States Army raised a large number of tank destroyer units during World War II. For most of the war US Army doctrine called for tank destroyers to primarily operate as concentrated tank destroyer battalions during combat. These battalions were to be concentrated in regiment-sized groups and brigades when needed to combat large forces of enemy tanks. However, combat experience in North Africa and Europe demonstrated that units larger than battalions were not needed. Tank destroyers were usually parcelled out to other units, and were rarely concentrated in battalions. The thirteen tank destroyer group headquarters dispatched to Europe never led massed units of tank destroyers, and nor did the 1st Tank Destroyer Brigade.