Would they even have lifeguards if they can breathe underwater and there’s no danger whatsoever?

If you didn't see this comic, probably ought to go read as it brings up the origin of his job: https://www.furaffinity.net/view/50493560/

The short answer is that the military is not exactly adept at spending money efficiently. The long answer (and information not really addressed in the comic) is that the bat wanted to join the Space Force but was not admitted due to poor eyesight. Wanting to find something for him to do, they found some other open position for him where they wouldn't have to worry about his actual performance. And the position exists because of some level of "lifeguard good so make them mandatory" that was not written in such a way that it allowed exceptions for cases where everyone can breathe underwater.

That’s really funny! Although, I suppose, I would’ve reacted a little more generously, than the comment with my tax dollars being at work. Considering the most expensive things in the military I think would be the provisioning to clothe feed and give medical care and hygiene, to troops along with acquiring and maintaining equipment would be the most expensive part. I would think that is where most of my tax dollars would be going into that basic upkeep. That being said if I was in a useless job like this and got really bored, I think I would start making snarky comments a lot to pass the time like some of the stuff you hear from that brilliant classic television show M*A*S*H. By the way, have you seen that before? One of the best shows ever in my opinion

Well making snarky comments can be a little intimidating when you around people much, much stronger and bigger than you. I have not seen MASH. Was certainly before my time and not something that either of my parents seemed interested in revisiting so it was never on.

If you get the chance I highly recommend it. It’s one of the best tv shows ever made

Adept at training and going to war but not adept at financial management and budgeting.

A number of veterans who have seen the comic/heard the backstory say the general idea feels quite relatable.

Really? How come?

In your words, "not adept at financial management and budgeting"