Doctor Dogs (1 HD, 1d4 healing lick, 1d2 bite damage)
These large, fluffy dogs instinctively rush to find and rescue people trapped in the rubble or wounded in the trenches. Made from a breed that once sought out those trapped in avalanches, it was genetically and magically altered to drool anesthesia and a disinfectant. It licks wounds to help heal injured soldiers, and is bulky enough to carry medical supplies and can also help carry wounded soldiers. It's bite is very weak due to their slobber helping heal their own inflicted wounds, and they aren't very aggressive of a breed anyway.
Elephant Hound (2 HD, 1d4 bite, prehensile trunk can use bigger weapons)
These incredibly intelligent dogs are mixed with elephants. They appear as dogs but with a long, furred elephant trunk attached to their face. They are often trained to use weapons, usually belt fed machine guns, mortars, and grenades they chuck after their handler pulls the pin- small arms tend to be too difficult to handle with their clusmy trunk, and they usually can't be trained to block bullets with swords like your typical enlistened swordsman. Fiercely loyal but independent. Smartest dog breed ever created, quickly becoming favorites outside of war too.
Messanger Pooch (1 HD, +4 AC when running, 1d4 bite)
These extremely fast and slim dogs are bred to deliver messages during the war. They are so fast and agile they are used to run across no-mans land during machine gun fire and bombing, since it's unlikely for the dog to get killed along the way. They can also crawl through pipes and have been sent halfway across the landmass to deliver covert messages too sensitive for radio.
Gremlin Dog (3 HD, 1d8 bite, +2 AC, 50% to just each ignore fatal blow)
Wrinkly dogs with sharp teeth and incredible pain tolerance. Very aggressive for both defending their owner and for attacking enemy positions. Gremlin dogs tear apart soldiers and are feared for their fighting prowess. They'll invade an enemy trench and bring back an enemy soldier's leg in their jaws while missing one of their own, tail wagging the whole way. If the dog's handler dies nobody will be able to get close enough to retrieve it, since the dog will defend their body. Used to great effectiveness when prying open the lid of a tank and dropping the dog inside to do its thing.