The Gunners are a hostile faction in Fallout 4. They are a mercenary organization with advanced military training and the largest mercenary group in the Commonwealth, being vastly superior than Raiders in discipline, organization, training and weaponry, but similar to them due to their hostile and brutal behavior.
Gunners are known to be extremely cold-blooded and lethal, accepting any kind of job for the right reward. A good example of one of their atrocities is the Quincy massacre, which purged Quincy of it's populace and nearly wiped out the Minutemen. Their main headquarters is Gunners Plaza, and they are primarily led by Captain Wes.
Gunners are similar to the Capital Wasteland's Talon Company, both being well-trained, well-organized and well-armed mercenaries who do not show a blink of mercy to the wastelanders. They act independently of any settlement, larger faction or person in the Commonwealth, and are openly hostile to factions such as the Minutemen. Gunners are also known for their extensive weapon arsenal, which includes firearms, laser guns, plasma guns and heavy weapons. Some higher-ranked Gunners are even known to use Power Armor suits.
There are numerous Gunner strongholds around the Boston ruins and the Commonwealth, but their primary HQ is the Gunners Plaza, a large building which was a pre-war broadcasting station. Their strongholds contain advanced defenses such as high-quality turrets, assaultrons, sentry bots and Mister Gutsies. Another notable Gunner stronghold is Quincy, which they took over after massacring the former settlers and driving the Minutemen out.
Gunner leaders are extremely skilled mercenaries, with their main leader being Captain Wes, and are known to don Power Armor suits and use lethal weaponry, which can even be Plasma guns or modified assault rifles. They are also known to use Stealth boys in combat, and when they aren't using Power Armor, they'll likely use modified combat armor.
Fallout: New Vegas