I don't think it's actually just arms and equipment. It means 'well-ordered.' It's the ability to call up organize and elect leadership from the people at need,

I don't think it's actually just arms and equipment. It means 'well-ordered.' It's the ability to call up organize and elect leadership from the people at need, among many other things. For example, Article I Section 8 provides Congress the power "To make Rules for the Government and Regulation of the land and naval Forces;" It's in a similar manner that the 2nd should treat 'regulated' militias.