Should the United States be invaded or be in imminent danger of invasion from any foreign nation or Indian tribe, or of rebellion against the government of the United States, the President may call forth such number of the militia of the State or States most convenient to the place of danger or scene of action as he may deem necessary to repel such invasion, or to suppress such rebellion, and issue his orders for that purpose to such officers of the militia as he may think proper. If the militia of more than one State is called into the active service of the United States by the President, he apportions them among such States according to representative population. In a time of rebellion the militia is subject to the same rules and articles of war as the regular troops of the United States.

When called into actual service, however, the militia is reorganized in a manner similar to regular troops. Each regiment of infantry then has one colonel, one lieutenant-colonel, one major, one adjutant (a lieutenant), one quartermaster (a lieutenant), one surgeon, two assistant surgeons, one sergeant-major, one regimental quarter-master-sergeant, one regimental commissary-sergeant, one hospital steward and two principal musicians; the regiment composed of ten companies, each company consisting of one captain, one first lieutenant, one second lieutenant, one first sergeant, four sergeants, eight corporals, two musicians, one wagoner, and from sixty-four to eighty-two privates. The militia is then also further organized into divisions of three or more brigades each, and each division has a major-general, three aids-de-camp, and one assistant adjutant-general (with the rank of major). Each brigade is made up of four or more regiments, and has one brigadier-general, two aids-decamp, one assistant adjutant-general (with the rank of captain), one surgeon, one assistant quartermaster, one commissary of subsistence, and sixteen musicians as a band.

When thus called into actual service, the President may specify the period for which such service will be required of the militia, not exceeding nine months. During the time of service they will be entitled to the same pay, rations, clothing, and camp equipage provided by law for the regular army of the United States. They are also allowed mileage for the distance between their places of residence and the place of rendezvous from which they start for the field of military operations, with forage for the animals of mounted regiments, loss of horses, etc.

Courts-martial for the trial of militia are composed of militia officers only.

National Armories

At each United States arsenal (or place where military arms and munitions of war are stored) is established a national armory, where muskets and carbines for the military service are manufactured. These armories are each in charge of one superintendent, who must be an officer of the ordnance corps of the army.