All Cat IVs first went through basic training before attending their Cat IV training program.  Most were not able to successfully complete first time through.  Some were recycled for second attempts and even third attempts.  A few made it but the majority was not able to do so.  Since they still had a service obligation to complete, they were assigned duties consistent with the basic training, which, for the Army, was primarily infantry. The Vietnam war was raging at that time and that is where the majority of CAT IV training failures were assigned.  About four hundred thousand men were brought into the armed forces for this failed social experiment until it was phased out in 1968.  They entered the armed forces with mental problems and were discharged with the pre-existing mental problems.   Many Cat IVs who served in Vietnam subsequently claimed their mental problems were caused by that service, which was total nonsense.  More to follow.