Essentially the largest mercenary group in the Commonwealth, the Gunners are a military-themed, well-organized and equipped group of for-hire killers with their own customs and signage who control numerous large strongholds in and around the Boston area. They were responsible for the dissolution of the Commonwealth Minutemen under Ezra Hollis at the Quincy Massacre. In 2287, Quincy remains one of their key bases of operations.
Similar to the Capital Wasteland's Talon Company, though non-hostile Gunners are sometimes seen protecting Caravaners. Going near their territory always results in a hostile reaction from its occupants much in the same way as common raiders. They differ from raiders in their lack of drug dependency, use of superior equipment (they commonly come equipped with combat armor and rifles), extensive use of laser weaponry and use of other heavy duty military gear, such as Assaultrons, Mister Gutsies and their commanders are even known to make use of power armor. Their lines also suggest much better training.
They also possess functional vertibirds, which they use to transport attack teams, usually composed of 2-4 Gunners, along with 1-2 attack dogs. Though they are a rare sighting, and seem to only appear south of the Boston ruins, and rarely to the north (e.g., settlement raids). Players should be especially cautious near the edges of the Glowing Sea, as a vertibird showing up there will either mean the BOS or a Gunners attack-team dropping in.
Many Gunners also get their blood types tattooed onto their foreheads by their medics. This is both a practical measure and a rite of passage. This can be seen on some, but not all, Gunners.
Judging by the Gunner's military style organization and access to considerable stockpiles of pre-war military equipment; the mercenary group may have been founded by remnants of the U.S military, similar to the Brotherhood of Steel and the Enclave.
Gunners, in some areas, will not openly fire on the Sole Survivor, though will appear hostile on the rader - instead they will warn them to back off, if the Survivor ignores them and approaches then they will become hostile and attack.