What branch of the military is the armored division in?

The US Armored Division was a division that was organized to be a mobile unit that used tanks. The US Army did not have armored divisions when Germany began its "blitzkrieg" attacks across Europe. The US have very few good tanks. The US Army organized the Division to have 2 Armored Regiments and 1 Armored-infantry (or mobile infantry) Regiment. Later, this organization was found to be too bulky. Also, they saw the need to have smaller mobile armored units to support the infantry advance- simliar to German panzer-grenadier regiments. US Infantry Divisions did not have any armored units as part of their organization. However, they eventually had 1 Tank Destroyer Battalion and 1 Anti-Tank Battalion or more assigned to them for support.