Dogs were often used as messengers, companions, and military working animals. The top left image below shows a dog providing medical bandages to a soldier. Since they have a keen sense of smell and excellent hearing, dogs were often used to find wounded soldiers.
Bottom left image shows a messenger dog with fitted spool harness for laying out telephone wires.
Bottom right image shows a dog handler reading a message brought by a messenger dog, who had just swam across a French canal.
Finally top right is of Stubby, the most decorated war dog of WWI, who started out as a mascot but became a full-fledged combat dog. Due to his acute sense of smell, he warned his soldiers of incoming gas attacks by running through the camp and barking, sounding the alarm. He saved thousands of lives also by locating wounded soldiers on the battlefield and even captured a German spy. Stubby received countless awards for his outstanding service.