The military could issue USB storage devices and identity tokens that keep their information internally encrypted and which only work on sirpnet-trusted computers.

Scenario: Anything copied to the USB device is internally encrypted, offline, with one of the military's public keys. This process requires no network-side authentication, but would require the soldier's "identity key" to also be plugged in and "sign" the contents.

Putting the storage device in a non-trusted computer means the contents are not retrievable.

To decrypt the contents of the device, you have to first authenticate to sirpnet from a trusted computer. It's then and only then that the computer is allowed to unlock the information on the removable drive.

This method is not safe to hardware reverse-engineering, but should be safe enough for operational use.