When the organized militia, or any part thereof, is called for active service of the United States under the Constitution and laws of the United States, the Governor shall order the same to service, and if the number available is insufficient, the Governor may call for and accept as many volunteers as are required for service in the organized militia and state guard. During the absence of units and organizations of the organized militia in the service of the United States, their state designations shall not be given to new organizations, and all organizations and officers on return from such service shall be given their former standing and rank.