As part of the Army or National Guard of course. Only federally regulated militias get 2nd Amendment protection (until they don't).
Especially in Massachusetts. It's ironic that Massachusetts, the birthplace of the American Revolution, has a state constitution that protects the right to keep and bear arms only as a collective right ("in defense of the state"). I know this is about the U.S. Constitution, but judges from Massachusetts probably can't help having been contaminated by Massachusetts' thinking. (Even so, it takes a lot of mental
legerdemain to pull an "only in the home" interpretation out of
Heller and
McDonald.)