Sensitive systems

When I worked on (UK gov) sensitive systems, it was a basic requirement that you had two networks - a blue network for classified material and a red one with Internet connectivity - with an air gap between them. E-mails discussing "where shall we have lunch?" went on the red network and the ones that read "we attack at dawn" went on the blue network.

This was all a few years ago, but I would hope that modern US military systems observe a similar distinction. Perhaps Lewis can tell us if this is still the case (or is the information classified)?