"The United States Cavalry, or U.S. Cavalry, was the designation of the mounted force of the United States Army from the late 18th to the early 20th century. The Cavalry branch became the Armor branch with tanks in 1950, but the term "Cavalry" such as "armored cavalry" remains in use in the U.S. Army for mounted (ground and aviation) reconnaissance, surveillance, and target acquisition (RSTA) units based on their parent Combat Arms Regimental System (CARS) regiment. Cavalry is also used in the name of the 1st Cavalry Division for heraldic/lineage/historical purposes. Some combined arms battalions (i.e., consisting of a combination of tank and mechanized infantry companies) are designated as armor formations, while others are designated as infantry organizations. These "branch" designations are again, heraldic/lineage/historical titles derived from the CARS regiments to which the battalions are assigned."
-Wikipedia