In October 2009, Congress passed the Military and Overseas Voter Empowerment (MOVE) Act.
This act states that, as an overseas/military voter, you should send in a new Voter Registration/Ballot Request form to your local election official every calendar year during which you would like to vote, as well as whenever you change your address. You should send this in as early as possible to ensure that you are registered in time for election day!
Never assume that your ballot will simply be sent to you without sending in a new Voter Registration/Ballot Request form, or having direct confirmation from your election official that you are on the voting rolls. Always confirm that you are on the list to receive an absentee overseas/military ballot for the upcoming election.