There's a single buyer that wants a particular missile, and multiple defense contractors bidding on right to supply it. At some point hopefully before, but sometimes after the bid is won, that contractor has to figure out how to make and deliver that thing, which is a standard manufacturing process involving a bunch of components and subsystems, some of which are made in house, some of which are bought of the shelf, and some of which are outsourced. That part's the supply chain.