If you are going to be 18, then you can do whatever you want. There is an old saying, its easier to ask forgiveness than to get permission. Its your life. Going to the Navy or AF isnt necessarly any safer than going into the army. Do what is going to make you happy. In any case, there is no guarantee you will get into the Army and no guarantee you will choose the Army. Its going to be a lot better for you to have three option (assuming they all say yes) than to close yourself off to one by not applying