I've heard that the DoD uses RHEL pretty extensively. RHEL in the US Military

That article says that the US military has the largest single install base for RHEL in the world, but that was about 15 years ago, I don't know if that's still true.

Apparently back then the US nuclear sub fleet and its sonar systems also ran on RHEL.

I suspect lots of military hardware runs some form of *Nix or BSD type system. Many embedded systems run some *Nix type OS, and a huge portion of the developed world's weaponry is smart, so it it full of low power embedded systems and custom SoCs.

Don’t look too deeply into this unless you’re comfortable discovering that the military and security state is a prolific contributor to many open source projects.

https://www.redhat.com/en/blog/red-Hats-decade-of-collaboration-with-government-and-the-open-source-community

When we rolled into Baghdad, we did it using open source. - Major General Nicholas Justice

Check out the World of Tanks forums for information.

There are many reasons Microsoft software is only "good" (and I'm using that word loosely) in business and home settings. Can you imagine a rocket taking off and windows suddenly "rebooting to complete updates" (or whatever it is that it says along those lines)?

Sadly yes, Linux kill

Greek military uses Linux Mint, so yeah, it's used in some places. I believe the Indian one does too.

Well I know my local army base (US) was looking for Linux sys admins, so I figure they have some servers on base.

as they're robust

I would argue they are just what was used during development. After that, it never changes.

Why did they use it back then? Were there many alternatives? I do not know.

I imagine they use it in much the same way as any enterprise. Running servers and workstations, mostly.

F16's run Kubenetes clusters.

Lots of individual bits of hardware on specialized devices will be running embedded operating systems. QNX is big in automotive for the same reasons it'd work on a rocket.

Linux is commonly used in the communications systems, like on invidual radio "stations". Propably used everywhere where high confidentiality and security is required.

We used it as OS for the tank and airplane simulators, just because it made them cheaper compared to buying 500 Windows licenses

Most of that information is actually publicly available.

Stuff like this https://www.usaspending.gov/search/?hash=624182a957cfea14bc90717fb91ec1f8

Didn't they at one point use a bank of PS3s when they still allowed for Linux boot options?

Looks like that are switching over from a generic Linux into android

Linux distro NixOS is used by mil-tech company Anduril

I saw a youtuber once reviewing the distro that the Russian military uses. It had some crusty retro desktop environment iirc.

Turkish military uses Pardus, a Turkish Linux distro, but I'm not sure to what extent.

When I was in the army the S1 desk jockeys were using dedicated word processors with 8" floppies. Get off my lawn! :-)

I'm not so worried about stormtroopers using linux as much as guns, bombs, prisons, cops, torture, genocide, nukes, etc.

Why are you asking? Yes it is used but obviously the exact systems are kept secret. As far as I know it is a mixed environment. I do know the US Air Force uses Kubernetes