I used to work as a mental health counselor in a residential facility and I would say the best thing you could do for him is speak to his parents about his behavior, being he is obviously NOT in a sound state of mind it wouldnt do any good to talk to him.
He can be committed IF he is a danger to himself or others, otherwise he would need to volunteer.
It would be best to get someone to convince him to go to the hospital so they can evaluate him and see if he is a threat to himself or anyone else. Has he ever threatened suicide? If he does contact the police and they will have him committed.
The best advice I could give you is TRY your best to get him evaluated by a professional.
One question: Did he go into the navy with these delusions? Or did they begin in the navy? Was this why he was released?
Schizophrenia affected people will usually speak in ways that you or I would have a hard time following , they have delusions of grandeur, sometimes they hurt themselves like cutting and can hear voices and these symptoms can vary in intensity from person to person so once again, do your best to speak with someone close to him who can get him evaluated.
Dont know if I helped but Good Luck and I hope everything works out.