It’s the public’s network, funded by tax payer money. The fact that they KNOW that they are global targets for cyber attacks and maintain so SO much publicly routable area is beyond irresponsible. Even more irresponsible is I’m positive they IP addresses are hard coded in some of those old systems.
The DoD has it's own private internet. Anything truly important isn't exposed to the public.
Then fork it. The difficult part is figuring out where the minimal cut is.