Information about PKI within the DoD
The Defense Information Systems Agency (DISA) has lots of information about the use of PKI within the Department of Defense on the part of their web site dedicated to Public Key Infrastructure (PKI) and Public Key Enabling (PKE). If you're interested in exactly how all that money that the DoD is spending on PKI is actually being used, this web site is a good source of information.
DISA even publishes The PKE Quarterly Post, a newsletter about all things PKI in DoD which actually seems to contain lots of useful and interesting information. Even if you're not interested in the use of PKI by the DoD, you'd probably find the amount of PKI activity in the DoD amazing. They're clearly spending lots of money on this.