So, Justice Scalia.
He says - and I actually tend to agree with him on this point - that the use of the word bear means that the Second Amendment only applies to weapons which can be carried, so there go your cannons, your missile launcher, your nuclear warheads.
He continues by pointing out the obvious next argument, which is "What about rocket launchers"? He doesn't give a direct answer to that, but he does say that the benchmark would be "What limitations are within the understood limitation that the society had at the time?" As the society at the time has no hand-held missile launchers, automatic weapons, flamethrowers, or bazookas, and they had only the most primitive of hand grenades, I feel comfortable with the level of strictness (or outright illegality) we have on these weapons.
The logical conclusion is that the Second Amendment was not written to allow the average citizen access to any and every weapon in the military arsenal, then or now. The entirety of the gun debate is arguing where to draw the line between allowable, and too much.