So there I was, at the first gunner guard post you run into

... I was sneaking around underneath it when I encountered that skanky trader Dreth and her two gunner guards at the little campfire spot almost directly below the outpost. So I traded with her to sell some stuff, and as soon as I ended it, the gunners in the outpost sensed I was there (because trading automatically takes you out of stealth) and went hostile. I immediately stealthed again, and became hidden right away (night time). But the guardpost gunners had already started shooting, and even though I disappeared, Dreth's gunner guards started shooting back at the gunners above, and the fight was on. Not sure who would have won, but I picked off the outpost gunners as they came around to attack Dreth and her gunner guards, so that ended it.

I just found it hilarious that the two groups of gunners were so determined to kill each other

I love those kind of things. In the last couple of days I've seen: Raiders vs. gunners; Yuo Gai vs. Glowing Ghouls; gunners vs. Deathclaws; and Deathclaws vs. Mirelurks. It's amazing actually. I really enjoy it.

But is it as epic as the one time I saw a Settler and Supermutant bare knuckle boxing, and then forming a temporary alliance to fight a Deathclaw?

There are places where several groups fighting eachother. I usual go to the location nearby where the supermutants with nuclear bombs stays and I make them aggro me. I run towards the other groups with the supermutant(s) follows me. The supermutants will soon loose track of me and instead attack somone else. I stay on distance and watch the fireworks.

Cheers,

-Klevs

Yeah. But it ain't often you see a faction fighting it's own members- when was the last time you saw raiders fighting raiders, or ghouls fighting ghouls?

Gunner on Gunner? maybe due to you having an interaction with them and them using stealth? Maybe guards above got suspicious of their cohorts?

Only thing I can figure is, once the gunners above spotted me and started shooting in my direction, Dreth's gunner guards' programming must have been to 'protect Dreth at all costs, regardless of what faction is attacking'. Fulfilling their contract to the letter, as it were. Even though they were mistaken, and it was me and not her the other gunners were actually shooting at. Guilt by proximity, I guess. Or perhaps Dreth returned fire first, as she is not a gunner, and her two guards programming again overrode their faction affinity and caused them to support her in the fight.

Last time I saw gunners fighting each other was the appetite for destruction tour.

Slashing at each other with Axel's ! LOL

This is best bet. Happens in Skyrim too.

For example, Dragon Priests are actually friendly to both Draugr and Dragon factions but the Draugr and Dragon factions aren't friendly to one another. Dragon Priests will primarily side with Dragons first, thusly causing the chance of Dragon Priest VS Draugr fights.

Dreth probably wasn't assigned to be friendly toward the default Gunner faction. Just the two Gunner Guards who is with her. So when she starts fighting with some default Gunners, the two Gunner Guards had her set as the primary ally thusly they sided with her in the fight instead of the normal Gunners.