I don't think branch really matters personally. There are tons of joint duty assignments. Plus, why would, say, a navy Guy in Hampton roads care if an air force Guy at langley looked out for his tank while he was tdy?
Actually, now that I say that, I'm thinking there are multiple bases in some cities. Might just want to break it down into cities or metro areas.
Its already going to be a small number of people, may not want to fragment it too much more.
Just my two cents.
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