During major conflicts of the United States prior to the twentieth century, Army leaders sought to find the best command level at which to merge infantry, cavalry, and artillery into effective, coordinated combat units. Brigades and divisions usually comprised a single arm, while the army corps was the basic combined arms unit. Within the army corps itself, little specialization existed beyond the combat arms. Usually no field units were organized for signal, medical, transportation, military police, engineers, ordnance, or other combat support services. Hired civilians or detailed soldiers provided such support in the field. By the beginning of the twentieth century, however, innovations in warfare, especially technological developments, required more sophisticated organizations, both to use the new technology and to integrate it into a larger operational and tactical framework.
