It seems like you already know about the military and not one of those people that wants to join for an action movie Call of Duty experience, so that saves me a lecture. But even if you really know you want to join the military after highschool, keep trying through the rest of your years, even if you're getting C's and D's because you may change your mind, being that you still have three years of highschool. Also you'll need the knowledge for when the military gives you a scholarship.