What paperwork mistake sends Richard Perry to Vietnam? What is ironic about the situation?

Richard Perry's medical file hadn't been updated. After suffering a knee injury, Perry was deemed unfit for combat duty. None-the-less, untimely filing left him open and available to be sent to Vietnam. This is ironic because his former captain had already told him, "it takes forever to process a medical profile". He captain wasn't kidding.

he didnt tell them he sucked dick so they had to keep him away from other guys