https://instagr.am/p/C_fpE-rODaq

Did the CO post the photos or did the NAVY PAO published the photos?

His PAO posted the photo and if you have rifles on board you should know how to properly employ them, even as the CO. I don't think he was specifically fired for the picture but it lead to an investigation which led to his firing.

You mean it's not protocol for the ship captain to be on the main deck shooting enemy threats with an M4 during an attack on the ship?

There was a lot of other stuff going on with that ship, especially persistant maintenance issues. Ship suffered a steering casualty which caused a breakaway during underway refueling.

From what I've read, the steering issues might not have necessarily been the captain's fault - they were apparently reported IAW standard protocol, a tech team was sent out, but the tech team were unable to isolate/diagnose the problem while the ship was in port, and the tech team didn't have authorization/budget to stay on the ship when it put back to sea.

So the ship went back out with the cause of the steering problem unsolved, and it kept happening.

IMHO, that's on Big Navy for not doing what was needed to address an issue that the captain had notified higher of IAW policy. Unless their position is that he should have refused to go out unless he could take the tech team along.

I assume Big Navy (which last I heard had more Admirals than boats) will keep running the management CYA playbook of scapegoat firings whenever anything draws scrutiny.

If congress was worth a damn they'd fire the admiral corps for the implication that they either
A. failed to raise the minuscule number of competent captains that this navy requires
B. are firing subordinates to avoid personal scrutiny