That's not actually correct, it says "arms", not "some arms". If you take guidance from the "militia" part (possibly dubious, as it's generally interpreted as a preamble), a militia, in a current defensive war, would require anti-tank and anti-aircraft rockets and missiles, at the very least. The problem with that is, in Heller, the militia is not really part of the test anymore. You might be able to argue against suitcase nukes, and they don't really have a defensive or targeted offensive purpose, and are only really useful for terrorism.