I am currently deployed overseas and set to return approximately a month after the tax deadline. How long do I have to file without an extension or do I need one?

You mention you are deployed so assuming you are deployed to a "Combat Zone" (see pages 15-16 of Publication 3) or in support of combat operations, you have at least 180 days after you depart the combat zone to file and pay taxes (see pages 28-30 of Publication 3) for more information on extensions available to military personnel.   

The IRS works with the DoD to identify personnel serving in Combat Zones or in support of Combat Operations. You do not need to file extension forms in those circumstances.