Maybe a volunteer fire department, Search and Rescue Unit or another local civil protection organization?

I'm volunteering at my local "Sea Rescue" station as a boat commander (not in the US). I feel like I'm getting similar things out of it, that are described in the article, namely

- leadership experience

- taking decisions under pressure

- contact with many different groups of society

- feeling like I'm doing something concrete to help my community

Even though I am sure Chris is a great guy and who is absolutely doing this for the right reasons, he mentions a "daring raid across the desert in Libya to rescue captured sailors". When you read about the dash, it ended with the "captors attempted to run away but were gunned down by the enraged British rescuers. The prisoners attempted to stop the killings but failed." Sure, that was a long time ago, but the guy commanding this raid still seems to be a fondly remembered role model for the squadron. Not because of the above war crime I'm sure, but they are overlooked in favor of a "daring dash". That is one of the issues I have with the military.

If you have a green card you can enlist. https://www.uscis.gov/military/naturalization-through-milita...

I believe French foreign Legion, YPG, and possibly the Georgian National Legion (operating in Ukraine) accept non-citizens, although none of these are in the US. There is at least one foreign legion protecting Yazidis that does as well.

You need to be a permanent resident or citizen to join the US military. As an H1B visa holder you can apply for permanent residence, but you wouldn't be able to join the military until you have received that status.

That's pretty close to being a mercenary.