Here's a story on the background to the Wikileaks episode, describing how the State Department linked up to the military's secure SIPRNET. It doesn't change my previous feelings about the need to track the usage history of each person authorized to access the network.
As a side note, back in the day at ASCS we were on the distribution list for State department cables, or at least some subset of them. Some were "Secret", some were not. Because I didn't have a security clearance I didn't routinely see them, but they came into the records management shop under some arrangement with the defense preparedness people in the agency. As I write, I'm becoming aware of how foggy my memory is, or perhaps how foggy my original understanding was. Were these cables from agricultural attaches, perhaps, and not defense related at all? Maybe.