What was the term used to identify officer personnel twice passed over for promotion who accepted an enlisted grade to finish career?

RIF, reduction in force. Past tense RIFed.

My dad (10th Mt. Div. WW2) was commission a 2LT in 1940 and fought in WW2. By 1955 he was a Major. Then the was a big reduction in force (RIF). In order to finish out his 20 years he enlisted. I was to young to know what they were called. He retired as a LTC. During his retirement ceremony some of his enlisted buddies were overheard to say something like, "hey, isn't that LTC up there Dave Arnold?" Apparently most of them didn't know he was an officer in the reserves.

ALL I knew/knew of were Reserve Officers in the Army of the United States and retained their Reserve Commissions. My Bn SGM at Fort Jackson in 1965 was an SGM USA and retired while I was there as a COL USAR. He was RIFed for over strength a couple of years after the Korean Police Action as a Major, AUS. Kept up his schooling, ie C&GS and eventually was a COL at retirement. Meanwhile, he became a Technical Sergeant E-2 or E-7, USA. Not sure when they reversed the pay grades and added two more. There were still MSGE7, SFCE-6, etc in the early 1970s. Army did ranks like MSGE7, MSGE8, SP4E4, etc so one would know rank and pay grade.