"During the Viet Nam War the Army offered a combination of Basic/AIT/Infantry OCS (as an enlisted man), then 2 years as a Lieutenant, in the Infantry or other branches."
A friend of mine was drafted, then did the above (plus Airborne). But I recall that to do OCS he had to re-enlist for 3 years.
He made it a 37 year career, retiring as Lt. General (3 stars)!! Ranger. Combat all the way.
The BrG boss man I worked for at CENTCOM went OCS when he was a PFC in the Army. He is now a Brigadier and I believe he is in line to get his 2nd star next year (I think).....
There was a short period before the big build-up for Nam where you had to re-up for 3 to get OCS. By January 1967, when they had the largest call-up in American history, they'd reduced the requirement.