Comment by _djo_

There are not just government e2e apps, but government-provided and customised smartphones specifically for them, like the DMCC-S programme. [0]

Some of the apps are listed in that brochure.

There's no excuse for using Signal on personal devices for classified conversations.

[0] https://www.disa.mil/~/media/files/disa/fact-sheets/dmcc-s.p...