I still never understood why Charlie sent his boys to military school, he didn't do that with his other boys...unless Oona put her foot down.
I believe it was originally Lita Grey's idea and Charlie went along with it. Evidently he told friends that he sent them to Black Foxe so they would learn to hate the military.
Ironically though they both went in the Army though I can't remember if they were drafted or went willingly, I wonder if being the son of Chaplin helped or hurt them in the military at that time when Charlie was getting a lot of bad press.
I believe they were drafted. Judging from Charlie Jr's account, neither of them were given any special treatment (he writes about nearly being killed a couple of times). I don't think the fact that they were Chaplin's sons ever came into play.
Many children of celebrities went there. Maybe it was a recommendation?