Wuala stores their files in Switzerland. I doubt that would meet appropriate defense standards.

I'm very intrigued by the fact that you actually want to use an external cloud based storage solution. I would have thought that defense would have required not to use a third party for remote file storage. The best solution would be to "roll your own" and set up something in a private cloud hosted in a datacenter that meets your requirements. If you are a VMware shop, you should seriously take a look at Horizon Workspace as it provides a Dropbox like product that would be a great fit. If you want to run this on a budget, check out OwnCloud. I use that myself to keep home/work documents in sync between machines and always wanted the equivalent of Dropbox but syncing onto my own servers.