"That it is the duty of citizens by force of arms to defend our government against all enemies whenever necessity arises is a fundamental principle of the Constitution.
"The common defense was one of the purposes for which the people ordained and established the Constitution. It empowers Congress to provide for such defense, to declare war, to raise and support armies, to maintain a navy, to make rules for the government and regulation of the land and naval forces, to provide for organizing, arming, and disciplining the militia, and for calling it forth to execute the laws of the Union, suppress insurrections and repel invasions; it makes the President commander in chief of the army and navy and of the militia of the several states when called into the service of the United States; it declares that, a well-regulated militia being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed. We need not refer to the numerous statutes that contemplate defense of the United States, its Constitution and laws, by armed citizens. This court, in the Selective Draft Law Cases, 245 U.S. 366 , page 378, 38 S. Ct. 159, 161 (62 L. Ed. 349, L. R. A. 1918C, 361, Ann. Cas. 1918B, 856), speaking through Chief Justice White, said that 'the very conception of a just government and its duty to the citizen includes the reciprocal obligation of the citizen to render military service in case of need. ...'
"Whatever tends to lessen the willingness of citizens to discharge their duty to bear arms in the country's defense detracts from the strength and safety of the government."
- United States v. Schwimmer, 1929. [With quotes from U.S. Supreme Court Justice Oliver Wendell Holmes Jr.]