Originally there were four armored cavalry regiments [bns]: 1st (III CTZ?), 2nd (IV CTZ), 3rd (II CTZ?), 4th (I CTZ).
5th and 6th were formed Dec 1963 (originally as 5th Armor Gp and 6th Mech Battle Gp; the former all-tank; both later reorganized as the others and redesignated armored cavalry regiments). At some point the goal became to have one per division. In 1965 the six regiments had 29 squadrons (five with tanks, three with armored cars, and 21 with M113 APC’s).
10 regiments were active by Mar 1966 and the goal was to raise 6 more (would give one to each active division, one each to the two planned divisions, and four more at one per corps). The two planned divisions were not actually formed.
18 regiments were raised: 1st, 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 10th, 11th, 12th, 14th, 15th, 16th, 17th, 18th, 19th, and ?
This ultimately gave one regiment per division and 7 separate regiments [in 1972, 7th was with 1st Div, 11th with 3rd Div, and 14th with 22nd Div; 3rd might have been with 23rd Div, and 19th was in MR 2]. Each corps formed an armored brigade by 1970 with the corps number (1st to 4th), which was intended to have two non-divisional armored cavalry regiments; the brigades might also control a divisional regiment for a specific operation. (When the 11th went to the new 3rd Infantry Division in 1971, this left a shortage.) A nineteenth armored cavalry regiment was at least authorized in early 1971.
20th Tank Regt was authorized 31 Jul 1971 and operational by end of Mar 1972. Two more tank regiments were authorized after the Easter offensive in 1972; one may have been designated as 21st.
During 1974, two composite battalions (M48 and M41 tanks and M113 APCs) were created at the Armor School (Thu Duc, near Saigon).