[numpad0]

They just didn't have enough of reserved general purpose connections for future use. I guess this woild be especially the case with the Russian modules, which were literally surplus Soviet manned space army outposts(such a thing do not make a lot of sense, they did it anyway).

[PaulHoule]

This one

https://en.wikipedia.org/wiki/Salyut_3

had a machine gun!

[Mistletoe]

What was the gun for?

[krapp]

Shooting American spacecraft. What else would it be for?

[necovek]

If it made pew-pew sounds (inside the station, obv), mission accomplished regardless of it actually being able to shoot anything down, up or everywhere.

[krapp]

The story that I read somewhere was that it was tested once but the recoil either damaged the station or it would have affected its orbit so they never tried it again.

There was also Polyus which was going to be an entire battle station designed to counter Reagan's SDI satellites[0], but it never made it into orbit. It had lasers, though.

[0]https://nationalinterest.org/feature/the-rise-fall-the-sovie...

[necovek]

If that test round of bullets came out at 1000m/s, I wonder where are they now?

They'd cover around 1.5 billion km (<1 billion miles), and be past Saturn's orbit if fired away from the Sun. But it would not achieve escape velocity on its own, and the station was obviously moving relative to Sun and Earth, so we'd have to account for it too.