One could flip that question around and ask: Why does China need the fastest machine? The significance of the story isn't that America no longer ranks first.

One could flip that question around and ask: Why does China need the fastest machine? The significance of the story isn't that America no longer ranks first. I believe that in general, the really fast machines serve one of two purposes-- simulating nukes (for example, to test new designs), and simulating global environment (for example, to improve climate predictions).