During World War I, the United States had no canine corps, but once we entered the war, our troops were the beneficiaries of military dogs trained by other countries.
Carrying messages was one of the important uses of dogs during this time. Telegraph and telephone lines were often cut by the enemy, and dogs were faster and were smaller targets than humans. However, it was no easy task. Not only did they have to run long distances, but the dogs had to overcome obstacles like getting through barbed wire and crossing rivers. Those that were trained for liaison work were expected to travel to a destination and then return with a reply.