These dogs were a secret weapon in the Pacific, giving the Marines ample time of an impending attack or ambush. The Japanese made it a point to try and kill the dogs and handler first, a tribute to their effectiveness.
The Civil War is full of stories of dogs in combat, although not an official weapon, they were apart of the war.
On the ugly side there was a breed that no longer exist today that is documented in use during the period. This was the Negro Dog, used to hunt down and sometimes kill humans.