Has anyone encountered the "Gunner Guard" yet? There's 3 total (1 already dead), found on a broken bridge overpass right next to the Lonely Chapel.

Yes, they were rather difficult. Till they got into a fight with the sons of atom

Yeah, the one on ground level gave me quite a fight even after I threw a couple of cocktails at him. Don't know if it was lag or glitch but the cocktail didn't have much effect on him, dogmeat distracted him while I let loose with a barrage of bullets. The other one on the overpass didn't put up much of a fight, because I didn't give him a chance to gun me down. There's no info on the them, just wondering who exactly are they?

I encountered some about 3 miles southwest of my Oberland station settlement under an overpass. They have a huge base in the northwest.