After obedience training, working dogs are taught to recognize and respond to a range of scents that are often associated with explosives.
Michael Paterniti, of National Geographic, writes that dogs:
... begin to practice an exercise known as "birding," which is designed to let the handler direct the dog's movements from a distance. First a handler unleashes the dog and orders it to move toward a hidden "bird launcher," a remote-controlled catapult loaded with a tennis ball. Adherence to voice commands and hand signals is crucial and often hard-won. When the dog comes close to the launcher, the handler triggers it, and the ball rockets into the air. The dog gives chase and returns the ball to the handler, who praises and pats the dog.
As dogs progress through these exercises, handlers begin to hide items that have been scented with explosive material in the surrounding area. The items are routinely placed both nearby and far away in order to train a dog to constantly scan its entire surroundings.
In the final stages of training, the launcher and tennis ball are replaced with just scent markings. After a dog locates a scent and returns, the handler rewards the dog with a rubber toy.
For dogs, this boils the searching of IEDs down to a game. This positive reinforcement conditions the dogs to search for explosives, while also solidifying the relationship between handler and dog.
Although dogs are not always entirely reliable, they perform a vital function. IEDs are the number one cause of death for soldiers and civilians in Afghanistan.
In total, there are more than 2,700 dogs currently serving in the military.