By mid-1963, original battalions numbered as 11th, 21st 31st, and 41st (one in each corps zone, which matched first digit in designation). 22nd Battalion raised at Duc My in II CTZ, and 32nd and 33rd Battalions at Saigon in III CTZ by 1964; there were also a number of separate ranger companies; these were absorbed into bns by 1965
By Mar 1965 there were 20 Ranger battalions (3 in I CZT, 4 in II CTZ, 8 in III CTZ, and 5 in IVCTZ); other designations in 1965 included 42nd, 44th, 52nd .
Three ranger groups (headquarters and three battalions each) were operational by the end of 1966 and four by Jan 1968.
These provide 17 battalion designations, so three are still missing.
In Oct 1970 Ranger organization stabilized at 7 groups (3 battalions each). Later, one of the border ranger battalions in the Delta was upgraded to mobile status, giving 22 battalions.
In 1974, the 8th and 9th Ranger Groups were raised. These were operational by Jan 1975.
Additionally, there was the 81st Airborne Ranger Battalion (three companies), which was a special reaction force associated with the US and South Vietnamese Special Forces. By 1967 it had expanded to six companies, and then or later became known as 81st Airborne Ranger Group.