What? You can't go to a polling station while you are deployed overseas..you have to use absentee ballots. That goes for any citizen not in CONUS.
Nothing is stopping you from absentee voting here anyways. Some of yall are acting like its some new thing that no one has every done. I'm not sure if its incompetence, laziness, or (most likely) a combination of both of those things which is leading yall to feel like it needs to be mandatory because muh vulnerable wimpy people! 
Just keep in mind you're dealing with the USPS..and that physically showing up and voting is way more secure than dropping a letter in a mailbox and crossing your fingers that it makes it to its destination.
That being said request your ballots NOW if this is the route you choose to take.