Any elector of this State who is in the service of the United States or attending an institution of learning, and by reason thereof is beyond the boundaries of this State, and who has not registered before or whose registration has been cancelled may, at any time, request from the county clerk of the county of the elector’s residence an application to register to vote. The county clerk, if satisfied that the elector is eligible for registration, shall forward the application immediately. The county clerk shall, upon receipt of the completed application, file it in the manner provided by law.