FirstNet is not the Military's private internet.
They just only started talking about using it - coordination w/ Base MP's etc. and local/state LE and first responders/ems.
FirstNet is the "public safety" data network for all First Responders, Emergency Services.
Owned and Operated by AT&T
It is funded by the States w/ help from the Feds (spectrum and shit). They had an option to participate, most are. It's for their comms, laptops in vehicles, IP radio and phones (4G)