Explicitly protected by the second amendment, but not enshrined as a part of the US defense policy in any meaningful way.

How about the frickin Federalist and Anti-Federalist Papers!!! Come on...do they even make kids read those anymore in our decrepit public education system?? Federalist Paper No. 29 directly deals with the need for a well-organized militia made of common citizens and a primary plank of the anti-Federalist platform was a strong protection for militias.