Sec. 2. When the proper authority or agency of the United States of America shall make application to the School Land Board describing the area which is deemed necessary for use in the National Defense said Board shall issue an easement or surface lease to the United States of America granting and conveying to it the free and uninterrupted use of the area described. Provided that before such lease or leases be granted in any county that the Board shall notify the County Judge of said county and shall fix a date for hearing at which time all interested persons may be heard in protest or otherwise. Such easement or surface lease shall be effective only so long as the area is used for the purpose of National Defense, and it shall cease and terminate and the State of Texas shall be revested with full title and possession of the area when same is no longer used for such purpose.