Vicious dog

Vicious Dogs are a nearly hairless species of wasteland canine, apparently Pitbulls. In Fallout 3 they replace both Wild and Mutant Dogs of the previous Fallout games as one of the only hostile canines a player will encounter.

Compared to other animals such as bears and cows, dogs have been relatively unaffected by the Wasteland's radiation (as can be seen by the lack of mutated canines).

Vicious Dog
Ruthless survivors of the wastes, these starving irradiated mutts will attack anything that moves, including you, unless you have aquired the Animal Friend perk. Some times they hunt in packs

Raider Guard Dog
This is a Vicious Dog that fights alongside its masters, Raiders; they are still affected by the Animal Friend perk.

Talon Company Guard Dog
These dogs will often be accompanied by their masters, none other than the infamous Talon Company Mercenaries, but are still affected by the Animal Friend perk, much like its Raider brethren.

Guard Dog (Operation: Anchorage)
Used as guards by the Chinese Soldiers in the Anchorage Reclamation simulation, and are unaffected by the Animal Friend perk, unlike Raider and Talon Company Guard Dogs. Guard Dogs are worth only 1 XP.They are identical to Dogmeat in appearance, even having the same eye color, one being blue and the other green.

Strategy
Vicious dogs by themselves are not very dangerous unless you are already badly injured or there are a lot of them, which most of the time they will be. They have a high perception and can easily detect you from afar. Don't be surprised if they sense you from afar or if you get attacked from behind by one, as they are quite sneaky as well.

Dogs are not particularly tough and one or two shots from a hunting rifle is usually enough to put one down. However, they move quite quickly and can easily close the gap between them and the player.

After obtaining the Animal Friend perk, they will no longer attack you or your party unless provoked. Having the second level of the perk is almost useless when dealing with these creatures as they attack just about anything anyway.

Loot

 * All Vicious Dog corpses will only contain dog meat.

Appearances
Vicious Dogs appear only in Fallout 3.