Your concern is justified

 

But,

It is going to be hard on you if you are mostly concerned about what benefit he is going to get out of it.  A lot of sacrifice is involved, for both of you.

If he joined to serve the country, to be counted on for his comrades in arms, he would have an easier time, than if he is there for the concerns that you have expressed here.

Your concerns make total sense, any sensible parent would have such concerns.  But you should be more concerned about whether he knows what he is getting himself into.  If he has a romantic ideal for what it shoud be like, he will be disappointed, or even crushed by reality.

Make sure he has an identity of his own, a healthy sense of himself as a person, so that he can hold his own in order to contribute to the team.  If he goes there to look for other people's approval to feel that he belongs to something, he will have a difficult time.

Have him read up on naval history, from John Paul Jones to Nimitz.  Also, on George Washington and the people around him.

Congratulations!  He has achieved so much so young.  You should be very proud of him.  We are all very proud of him.