D2879 removed the usage of the advanced and elite war dogs, making them no longer use the fancier variant
Quick request changes over the _b thing that can be deleted now.
Here's how they look:
I think the chainmail is completely undistinguishable from cloth armor at a distance, so it looks fine to my eyes, and having some variety doesn't really hurt.
According to Wikipedia there should be sources that attest of the armoring of dogs https://en.wikipedia.org/wiki/Dogs_in_warfare. Maybe in some of the classical sources there is mention.
Gifts of war dog breeding stock between European royalty were seen as suitable tokens for exchange throughout the Middle Ages. Other civilizations used armored dogs to defend caravans or attack enemies.
In ancient times, dogs, often large mastiff- or molosser-type breeds, would be strapped with armor or spiked collars and sent into battle to attack the enemy. This strategy was used by various civilizations, such as the Romans and the Greeks.
None of that is sourced. Moreover, armour does not necessarily mean chain mail. It's not even clear if Britons actually used body armour (ask @genava55), so why should their dogs?
Britons did use body armor, chainmail is attested (Kirkburn).
Concerning the war dogs, there are more references here:
Strabo is a good source on the case: "Most of the island is flat and overgrown with forests, although many of its districts are hilly. It bears grain, cattle, gold, silver, and iron. These things, accordingly, are exported from the island, as also hides, and slaves, and dogs that are by nature suited to the purposes of the chase; the Celti, however, use both these and the native dogs for the purposes of war too."
However, no reference about any armor. I think this is made up. There is no account and there is no archaeological evidences.