Speaking about US defense companies, I'd simply call them "military/defense contractors" since most of them do development and manufacturing in-house. However, seeing that back in the old country the development was mostly the prerogative of all those countless NIIs that did not handle manufacturing themselves, I guess you are better off with the above. Or you could call them weapons design facilities in line with your own thinking. I do think though that "weapons" does a better job here than "military".