Applicants who scored next to the lowest on the entrance exams. Under normal circumstances they would not be allowed to enlist but during times of war and when recruiting was difficult a number of them were allowed to join. (background) In the 1960 the Pentagon was forced to accept some social engineering called Project 100,000 in which a great number of Cat 4 enlistees were taken in–the military has yet to recover. For classification purposes the category was further broken down to 4a, 4b or 4c which were defined by recruiters as “animal,” “vegetable,” or “mineral.”