2.--_As Trench Dogs or Sentinels._ The sentry or trench dog is trained to stay in the trench itself or in a small "listening-post" made for him, either on the edge of the trench, outside it, or at a little distance away. There he remains on the _qui vive_, ready to signal the least suspicion of a noise or the presence of the enemy. In this work both his eyes and his scent help him. He is kept on the leash, and he gives the signal of danger by a slight growl, without barking, which would give the alarm. The greatest difficulty in the training of dogs for this work has been to rid them of the habit of barking, but this has been overcome with care and patience. The training of dogs for this class of work can be--and has been--carried to great lengths. A man crawling on patrol work can take a dog with him, also in a crouching position, on a leash. A little tug at the leash causes the dog to rise, to retire, or to change its direction, and a properly-trained animal will answer to the leash as satisfactorily as a horse does to the reins. Such a dog is of immense help at night, when he can be taken quite close to the enemy. 3.--_As Patrols or Scouts._ The dog accompanies the human scout in his reconnaissance, and helps in finding advance posts or sentinels, and locating small groups of the enemy. 4.--_As Couriers or Messengers._ The animal acts as a messenger, carrying written orders or information, and is used according to circumstances. He can carry messages between groups in the rear and fighting formations in the front--for example, between the artillery and the infantry, and _vice versa_; between two fighting forces, such as battalions, companies, or sections; between the headquarters and the various positions of the army; or between the main body and detached posts, such as patrols, scouts, etc. Taken along by a patrol or scouting party, he can be sent back to the main body with a message fixed to his collar. The note having been removed and read, a reply can be attached to his collar, and the dog sent back to the original body of men, even if they have changed their position, since he finds them again by his scent. A dog is not only much quicker in carrying these messages than a man, and can cover ground where no cycle could go, but he also has an advantage in being almost invisible to the enemy. If on a leash, he can conduct a man in charge of reinforcements or ammunition to the new position of the patrolling party--sometimes over a distance of several miles. 5.--_As Dogs of Communication._ This is the most difficult task to which military dogs are put, and requires very special qualities, so that only a very few animals have been found capable of the work. It consists in sending him after a patrol _en route_ with a message, or even in finding a lost patrol or scouting party and bringing it back to its base. It will readily be understood that an exceptional scent is required in a dog to do work of this sort.