The Vietnam War was the first combat opportunity for "mechanized" infantry, a technically new type of infantry with its roots in the armored infantry of World War II, now using the M113 armored personnel carrier. In addition, armored cavalry squadrons in Vietnam consisted largely of M113s, after replacing the intended M114 in a variety of roles, and armor battalions contained M113s within their headquarters companies, such as the maintenance section, medical section, vehicle recovery section, mortar section, and the scout (reconnaissance) section. United States Army mechanized infantry units in Vietnam were fully equipped with the M113 APC/ACAV, which consisted of one headquarters company and three line companies, normally with an authorized strength of approximately 900 men. Ten U.S. mechanized infantry battalions were deployed to Vietnam from 1965 until their departure in 1972.