Original quote from US Bill of Rights: " 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." The clause about the militia is irrelevant and does not in any way modify or restrict the main point.
All individuals have the right to self-defense under the Non-Aggression Principle, and therefore also the right to purchase, keep, maintain, train with, practice with, and if necessary, use, any weapons they reasonably feel appropriate. It doesn't matter whether or not they are " regulated" or in a " militia" or what kind of weapons are involved. It doesn't matter whether someone has a knife or a nuke (as long as, for example, they take adequate safeguards to prevent exposing anyone to radiation or leakage or causing pollution) - if they hold or use their weapons only for defense, not aggression, that's their right. It also doesn't matter who the potential aggressor is (individual, group, organization, or government) that they seek to defend themselves against - even the government - especially the government, as the founders of America pointed out. No one else, including government, whether in peace, war, disaster, "national emergency", or any other excuse, has the right to restrict, regulate, license, confiscate, outlaw, or otherwise limit their weapons as long as they don't violate NAP. The right of every individual to keep and bear arms, as part of the right of self-defense, is an inherent right in relation to all others, not just government. The only exception is as part of a sentence after conviction for a crime, in which case the prison or other relevant authority becomes responsible for the convict's defense as needed.
Private individuals acting alone, and private militias, are answerable only to themselves and those they serve, as long as they don't violate NAP. If the rest of this Constitution authorizes any levels of government to create or maintain their own militias or other military forces, or obtain the use of such by contract, each level of government may command only its own forces, never the forces of other levels or of private forces, although of course thay can work together voluntarily.