The commander in chief may at any time, in order to execute the law, suppress riots or insurrections, or repel invasion, or aid in any form of disaster wherein the lives or property of citizens are imperiled or may be imperiled, order out the National Guard and the inactive National Guard or any parts thereof, or the whole or any part of the unorganized militia. When the militia of this Commonwealth, or a part thereof, is called forth under the Constitution and laws of the United States, the Governor shall order out for service the National Guard, or such part thereof as may be necessary; and he may likewise order out such a part of the unorganized militia as he may deem necessary. During the absence of organizations of the National Guard in the service of the United States, their state designations shall not be given to new organizations.