Here is another mention of the shortage almost 40 years ago.
“Security staffing of the facilities with improperly trained military police also posed a major problem. The MP Corps in Vietnam severely lacked the needed number of personnel trained as MOS 95C Correction Specialist. The temporary fix was to pull line duty MPs trained as MOS 95Bs Military Policeman, from field units and assign them to the facilities creating major disruptions in the ability for their parent units to perform their missions. In 1971 to address the problem at DHAC the 18th MP Brigade reassigned the 300th MP Company (95th MP Battalion) from line duty to correction duty at the DAHC.”
Correction duty must be a rough assignment. It's one thing to do what you're told, and still do a good job; another to re-up for something that burns you out.