Cyberdog

Cyberdogs, also called cyberhounds, are mechanically enhanced dogs found in the wasteland.

Background
 Technologically advanced organizations such as the pre-War United States government, the Enclave and Big MT developed the creatures. Big MT created weapons like the K9000 cyberdog gun which used a dog’s brain as its central processor and could sniff out and lock onto targets. Denver in particular had a large supply of cyber police dogs, and they still roam the streets. 

Characteristics
Cyberdogs are also called "K-9 units." They are not affected by pulse weapons. Their brains are subject to neural degeneration, but can be swapped out. If cyberdogs die, it is possible for them to be reconstructed or fixed, as seen in one of Roxie's endings. Cyberdog models include Mk. II and III, differing in appearance. Unique models include K-9 and Gabe. K-9 was created by the Dr. Schreber in the Enclave outpost of Navarro and based on the "Cyberhound Mk II personal security model."

Robodog
Robodog is a cyberdog, more specifically "Cyber-Hound Mk II personal security model." Dr. Henry brought it from the Enclave Oil Rig and settled down in the NCR.

Cyberdog
The military cyberdog has a sonic bark used as a weapon, and has a chance to knock down the player character with its melee attack. They also appear to have the ability to repair themselves.

Cyberdog
A slightly weaker variety of the military cyberdog. They can be distinguished from military cyberdogs by their black and white paint, as well as the red and blue reflective patches on their backs.

Named cyberdogs

 * Rex - The King's cyberdog and the Courier's possible companion.
 * Gabe - An oversized hostile cyberdog, genetically modified by Doctor Borous found in the X-8 research center.
 * Roxie - A temporary cyberdog companion that can be created in the X-8 research center.
 * K-9
 * Robodog

Appearances
Cyberdogs appear in Fallout 2, Fallout: New Vegas and the Fallout: New Vegas add-on Old World Blues.