At the always interesting blog "The Volokh Conspiracy", David Kopel has dug up a 1942 decree by Maryland governor Herbert O’Conor calling on armed citizens to serve in a reserve militia to defend the state against Axis "parachute troops, saboteurs, or organized raiding parties" or the actions of "enemy sympathizers within our State". It's notable for its plain statement that volunteers would be expected to provide their own weapons and would be expected to have basic competence with them -- even at this relatively recent date when the standing army was well-established as a tool of American imperialism and the foundations of the military-industrial complex had been laid.
This is what the "well-regulated militia" in Amendment II means -- a citizen body familiar with the use of arms is necessary for the security of the nation. ("Well-regulated" here does not have the meaning of "subject to extenisve regulatory law" but rather "effective and precise" -- in the same way that a mechanical timepiece is "regulated". In order to have people familiar with arms, it is necessary for the people to have them. Therefore, the Second Amendment tells us, the new nation shall not interfere with the vitally important -- not just for individual liberty but for the security of the nation -- natural right of the people to arm themselves.