Although most states allow use of an expired driver’s license with a military ID, Germany does not. A current, valid stateside driver’s license is required to get a USAREUR driving permit and international driving permit. Ensure your U.S. license is valid before you PCS.
If it will expire during your assignment in Europe, learn what your state’s requirements are to renew on-line (if possible). Getting a driver’s license in US is faster, easier and much less expensive than getting a license during your assignment in Europe.