A large network by definition cannot be air gapped.
I'm sure if you are able to design a network spanning the continental US, Hawaii, Alaska, US Territories, US bases around the globe, allowing both military personnel, civilian workers, contractors and suppliers to securely connect to it while being both economical on any order of magnitude close to the current cost and being effectively "air gapped" and secure the pentagon would award you a contract to build it in a heartbeat.
Until then let's all stop being literally arm chair generals and assume that while it surely has allot of room for improvement someone at the pentagon might just know what they are doing and they are doing the best as they can or fairly close to it considering all the constraints they have to operate against.
I'm sure if you are able to design a network spanning the continental US, Hawaii, Alaska, US Territories, US bases around the globe, allowing both military personnel, civilian workers, contractors and suppliers to securely connect to it while being both economical on any order of magnitude close to the current cost and being effectively "air gapped" and secure the pentagon would award you a contract to build it in a heartbeat.
Until then let's all stop being literally arm chair generals and assume that while it surely has allot of room for improvement someone at the pentagon might just know what they are doing and they are doing the best as they can or fairly close to it considering all the constraints they have to operate against.