Soldier..you can make a decision to serve your country, you don't need permission from people on this board to purchase a M5, let alone a used one.
I say, save every penny from now until you finish your tour. Who knows, you might come back with 100-150k in your account and have a change of heart at that time. If I were you, I would start saving for it now. Whatever you do, make sure you don't get away from your goal and dream..
Good luck and thanks for serving!