It's a well known fact that after original Internet becoming very popular US military has their very own separated, isolated and operated military network based

It's a well known fact that after original Internet becoming very popular US military has their very own separated, isolated and operated military network based on the similar design of packet switching of the Internet for their own use cases. Since it's operated by military they can make the networks infrastructure military grade and make the power supply to be fully redundant, but then Cold War was turned into just propaganda machine so perhaps there is no real motivation to make it really reliable. It's also a very common practices in many countries to have isolated and reliable nationwide network infrastructure for emergency usages for example disaster management purposes including military operations.