Sniffing around for 3,000 years.

Introduction
It is true — war dogs served the Egyptians, Greeks, Persians, Britons, and Romans. They served as sentries, area security patrol dogs, and attack dogs. Atilla used large dogs in his campaigns, and these were often gifted among European royalty. Frederick the Great used them to carry messages, and the French used dogs to guard naval installations in the 1700s.
In East Asia, the 15th-century Vietnamese emperor Lé Loi raised a pack of over 100 hounds, tended and trained by Nguyễn Xí, whose skills earned him a promotion to the emperor’s commander of shock troops.
The first official use of dogs for military purposes in the United States was during the Seminole Wars. Union troops routinely destroyed packs of bloodhounds because they were used for hunting down runaway slaves. In the Civil War, hounds were employed to pass messages and guard prisoners. During World War I, dogs were used as mascots in propaganda and recruiting posters.
In the Marines — World War II
The Marine Corps decided to experiment with war dogs in the late summer of 1942. A new turn for the Marines, but not for the dogs — as I said, they’ve been doing warfare things for a long while. The only question was, should they use Mastiffs, as did the Romans — or Shih Tzu, like the French?
Previously, in the 1920s, a Marine serving as an officer in the Garde d’Haiti trained a dog to work at the point of his combat patrols to alert him to bandit ambuscades. Marine historians believe that it’s probable that this Marine’s experience was later responsible for suggesting the use of dogs in jungle warfare (Small Wars Operations).
In World War II, the Marine Corps war dog training program was initiated at the direction of the Commandant of the Marine Corps, who directed the Commanding General, Training Center, Fleet Marine Force, Marine Barracks, New River, North Carolina (designated Camp Lejeune in December 1942) to initiate a training program for dogs when personnel and material become available. Shortly after, one officer and 19 enlisted Marines began training at the Fort Robinson, Nebraska, dog school. Four additional Marines began temporary duty at Fort Washington, Maryland — also in connection with training dogs.
The plan was that upon completion of training, Marines in Nebraska would return to Camp Lejeune, each with two dogs; the Marines at Fort Washington would return each with two messenger dogs. An additional twenty dogs would be procured by Miss Roslyn Terhune, given obedience training in Baltimore, and shipped to Camp Lejeune by the end of January 1943.
After procuring sixty-two dogs (42 from the Army), the Marine Corps received additional animals from various sources (Dogs for Defense, Inc., Doberman Pinscher Club of America, and private individuals willing to offer their animals as donations to the war effort). These were the primary sources of procurement of Marine Corps war dogs until 1 March 1945. After then, the Marine Corps and Coast Guard established and operated a joint procurement agency.
Marines considered an animal’s breed of secondary importance to the general excellence of war dogs. Still, the breeds found most suitable for German Shepherds (Alsatians), Belgian Sheepdogs, Doberman Pinschers, Collies, Schnauzers, Airedales, Rottweilers, and some mixtures of these animals. Other breeds could be acceptable, provided the individual animal met the required specifications in other respects.
Dogs accepted into the Corps had to be one to five years of age, of either sex, 25 inches high, weighing at least 50 pounds, pass a rigorous physical examination, and be proven not to be gun shy.

In the earliest days, the Marines highly regarded the Doberman Pinscher, rightly or wrongly, because:
(1) It was generally believed that the shorthaired Doberman was more adaptable to the heat of the tropics than many of the long-haired breeds (dog experts and fanciers held divided opinions on this point)
(2) Dog handlers were almost unanimous in their praise of the Doberman Pinscher and the German Shepherd for scout and messenger work; and,
(3) In the early days of the war dog training program, the Doberman Pinscher Club of America procured a large proportion of the dogs enrolled, which means that the emphasis was on Dobermans — hence an early preponderance of this breed over others.
However, the Marine Corps clarified that it had not established a policy favoring Doberman Pinschers over any other breed. In early 1945, the Marine Corps declined an invitation to have some of its Dobermans participate in a show out of concern that others may interpret that the Marines preferred one breed over another.
Most of the first dogs shipped overseas (the 1st War Dog Platoon) were Doberman Pinschers; the remainder were German or Belgian Shepherds.
When the Marine Corps initiated its war dog program, the Army, Navy, and Coast Guard had already instituted working dog programs with established training centers with several training programs for different purposes. The Marine Corps, however, is a combat organization. Senior officers saw no point in dedicating manpower resources unless dogs contributed directly to killing the enemy or reducing combat casualties. Consequently, Marine war dogs were confined to two types:

Scout and messenger dogs. At that time, the 1st Marine Division was still fighting on Guadalcanal. It was apparent that the South Pacific plans of the Joint Chiefs of Staff for a march up the Solomons chain meant that Marines would continue to operate in jungle terrain for a while at least, where concealment by the enemy was relatively easy. Infiltration tactics were the order of the day.
At first, it was difficult to find trainers thoroughly appreciating this combat angle. Marine planners initially selected trainers because they had civilian experience training dogs. Senior officers at HQMC visualized this program as one involving dog training — for training dogs rather than teaching them for a combat role. This lack of appreciation for reality training made combat Marines hesitant to volunteer for the program. It soon became apparent that if dogs were to be helpful in combat, their trainer and handler would have to be good combat Marines, capable of scouting and patrolling, with the dog being the means of increasing the radius of operations.
At the same time, operations officers understood that tactical situations might dictate a need for messenger dogs, and the best animals for that mission were the Dobermans and German Shepherds. There were other great breeds, as well — it was only that Dobermans and Shepherds performed in a consistently exceptional manner.
The training cycle at War Dog Training Company (Camp Lejeune) lasted 14 weeks. Selection for specific skill training took two weeks — and a time when dogs and Marines became acquainted with one another. Two Marines, selected for their experience in handling dogs, were assigned to each dog as trainer and attendant — a relationship carried into combat: two Marines and their dog forming a “dog unit.”
The next six weeks were devoted to training the dogs to interpret and obey the various commands and to familiarize the men with their dogs’ mental workings and reactions. Successful training was accomplished only through intelligent, patient, and sympathetic handling and treatment, and the chief reliance was made solely on praise and scolding. The final six weeks of the course were given to more advanced work, including combat work, which meant attacking any person or place the dog had become alert on command.

The initial advanced training for scout dogs started with the dog being fastened to a chain fixed to a post or wall with his handler beside him. A stranger approached threateningly, the handler commanding the dog to “watch.” When the dog showed aggressiveness towards the stranger, the latter ran away, and the handler praised the dog.
As training progressed from day to day, the dog was shifted from the chain to the leash in the hands of the handler, and the work was continued until the dog attacked persons, first on the training field and later in the woods or jungle. In the end, the dog was always alerted to discover the enemy when put on “watch” by his handler. The manner of his alerting could take various forms, one might strain at the leash, another show general excitement, another by crouching. Whatever the method, the handler, during the training, learned to “read” his dog’s reactions and act accordingly.
Messenger dogs were trained by first having one of the handlers move away a few yards. The other handler then put the messenger collar on the dog and ordered him to “report.” The first handler then called the dog and praised him when the dog reported. By slow degrees, the distance between the distant handler and the dog was increased until the former was out of sight and sound. Finally, the messenger dog would travel several miles from one handler to the other. This way, communication could be established between patrols, outposts, and the command post.
Throughout their training, the dogs, both Scout and Messenger, and their handlers were regularly subjected to small arms and high explosive gunfire.
The dog handlers were selected for their intelligence, character, physical ability, and any previous training as scout snipers (without dogs). When such men were unavailable, they had to be trained as scout-snipers concurrently with dog handling. Since dogs, from the point of view of training, can only respond successfully over limited periods, it was possible to spend half the time of the men training dogs and half the time training the men as scout-snipers. Paradoxically, the dog on duty could outperform a human in alertness, lack of sleep, and general condition, but in actually learning his lessons, it was found necessary to give frequent breaks and not spend too many hours a day on the lessons. Previous experience as a dog handler was not a prerequisite, but men who had associated with animals and had that indefinable ability to read their minds and understand them were the most successful.
No known means of compelling a man to be an expert dog handler existed. Many of the best handlers came from farms that had handled hunting dogs and farm stock. Some men soon learned they were not war dog men and were immediately transferred to other duties. In the same way, the dogs demonstrating that they did not have the qualities of a war dog in the Marine Corps were returned to their former owners.
Before leaving the War Dog Training Company at Camp Lejeune, the men, and dogs were formed into platoons consisting of 1 officer, 65 men, and 36 dogs (18 scout and 18 messenger). One man was assigned to each of the 18 scout dogs as handler, and two men to each of the 18 messenger dogs as handlers. The unit was further divided into three squads composed of 6 scout dogs — 6 handlers, 6 messenger dogs — 12 handlers, and a noncommissioned officer in charge. In addition, there were six supernumeraries, two for each squad, which provided relief for the regular handler in case of illness or casualty, and a platoon sergeant.
Each Marine infantry regiment incorporated a war dog platoon. An officer serving on the regimental staff became the Commanding Officer’s advisor in using dogs and commanding the platoon. The tactical use of the dog platoon always depended upon the mission of the regiment and its subordinate units. The war dog platoon could be employed as a unit or subdivided as needed.
The first Marine Corps dog unit sent to the Pacific was the 1st Marine War Dog Platoon, arriving in the South Pacific on 11 July 1943. This unit went into the Bougainville operation while attached to the 2d Marine Raider Regiment. Marine Raiders were enthusiastic over the performance of the war dogs during Bougainville.
Marine War Dogs also served on Guam, Iwo Jima, Okinawa — and during occupation duty in mainland Japan following the surrender.
In Vietnam
The Vietnam War introduced American troops to a new kind of warfare. Patrolling inside thick, triple-canopy jungles was dangerous by day and even more perilous by night. Enemy fighters used the jungle to their advantage, employing guerilla tactics (such as ambushes, mines, tunnels, and traps) in ways that U.S. troops hadn’t encountered before. A well-trained dog became an extension of his handler’s senses — seeing, hearing, and smelling otherwise undetectable danger.
The German Shepherd (Alsatian) was the most common service dog in the Vietnam War, used for scouting, sentry duty, mine/tunnel detection, and water patrols. Labrador retrievers were also widely used, primarily as trackers. Dogs were trained to alert their handlers to hidden dangers, from snipers to tripwires and weapons caches. Dogs could even detect enemy fighters submerged in rivers, breathing through hollow reeds, and waiting to attack American watercraft.
War analysts claim that these animals (and their handlers) are credited with saving as many as 10,000 U.S. lives and preventing certain injuries for countless more. They were so effective that they became special targets for the enemy, who began attacking kennels and offering bounties for the shoulder patch of a dog handler or the tattooed ear of a service dog. Many handlers wanted to bring their dogs home to America when the war ended. But in a decision by a Democrat-run Defense Department, these dogs were classified as equipment. At this time, dog handlers were not allowed to adopt their animals. Most animals were left behind, transferred to the South Vietnamese Army, systematically euthanized, or abandoned. America’s war dogs were the only combat troops that never went home.