Um, I work in a similar secure area, and these devices have been banned for quite some time.
Only a tiny fraction of DoD networks and personal computers are classified. It’s not like the B-2 bomber blueprints and the complete war plan against West Bumble are on every computer.
Probably the biggest problem for the classified networks is the fact that there are a lot more classified computers than classified computers connected to a classified network. Thus, people had thumb drives used only for classified information, that were locked in secure storage every night, so they could transfer files to the computer where they actually sit and do their work.