The Black Dogs or Hellhound are beast natives of the Special Region, ranked B among the Special Region's harmful animals, which have the appearance of a dog but the size of the tiger. During the Imperial Civil War, Zorzal's force uses these creatures as weapon to attack the JSDF and the Empire Loyalists in (a swarm attack or in swarm attacks). Like a wolf, they often hunt in pack and use sheer number to overwhelm an opponent.
Despite their beast like features, they stand no chance against firearms. It also shown that they are also extremely reckless and foolhardy since none of them try to retreat after JSDF's helicopters bombard on their position that kills hundreds of them, unlike others predators like wolf, lion or tiger, which often retreats after encountering hunters with rifle in their hand.
They are controlled by silent pipes (high frequency like dog whistles) "As Helm played an inaudible note, he paused briefly to respond, “This is to save our lives too. It might not do much, but I want to give the enemy some trouble.”
After saying that, Helm continued playing the silent flute." http://skythewood.blogspot.sg/2016/09/GJ71.html