Actually History and History International show military themed programming all the time. Just not ALL the time, if you catch my drift. The Military channel is owned by the same company as the History channel, and they might have more of what you're looking for if you want military type stuff 24/7. I watch these channels very frequently as I do things on my computer (mainly as background noise that I only pay close attention to when something interesting is going on).
Now Discovery has a lot of blue collar job or science based reality TV on it. I find some of that entertaining as well, personally, but you won't find what you've described on Discovery very often. For more of the science stuff that used to be on Discovery, you've got National Geographic channel, Net Geo Wild, Smithsonian channel, Planet Green, Animal Plant, and of course, the Science Channel.
You can't just get everything you want to watch in two channels any more. Every channel has branched out, not put all their eggs in one basket so to speak. My DirecTV bill is also quite a bit higher than I'd like, but hell, I like these channels and get the upgraded package (other than Smithsonian, which I mentioned but don't get).