Puppies which are deemed suitable for K9 training start their training early. They undergo rigorous training which includes obedience and socialization. Then, puppies start to learn more specialized tasks.

Police dog trainers carefully select puppies which they feel are right for the job. Certain breeds, like the German Shepherd, have natural tendencies which make them excellent choices for protection and patrolling. But not every puppy is the same, and trainers must carefully consider whether each individual puppy's personality is right for the job. 

Police service runs in these puppies' bloodlines - both of their parents were police dogs. It's likely that these puppies will be trained to be K9s after they've had some time to grow up. 

Even though puppies may make it into police dog training doesn't mean that they'll become K9s. Puppies and dogs are tested after every stage of training. If they fail, then they won't progress in their training and won't become K9s. 

Police often need new dogs as current police dogs retire. The Northumbria Police, based in Newcastle Upon Tyne, UK, currently employ 55 police dogs in their force. With dogs continuously aging out and retiring, it's necessary for the police to maintain an active recruitment and training program to keep up with the demand.

Meet Tuco. In this photo he's just 9 weeks old, but he's trying on a bulletproof vest that he'll grow into, with time. Officer Troy Casey, who is a 22-year veteran of the police force and Head Trainer for the Boston Police K-9 Unit, will train Tuco and prepare him to serve the city of Boston. 

According to police dog trainer Stephen Parent, police dogs are frequently trained using commands in German. Because German is not widely spoken in the United States, this helps to ensure that the officer can maintain control of the dog and no one else can give a command that the dog would understand or listen to.

Police dogs are trained to perform a wide variety of skills necessary to their service. Dogs are either "single purpose" or "dual purpose." Single purpose dogs provide the human officers with backup, personal protection and tracking talents. Dual purpose dogs do all of the same tasks a single purpose dog is trained to do, but they're also trained in either explosive or narcotic detection.

When police forces need a dog, they can choose one of two options. They can buy a readily trained dog, or may buy a young dog and send an officer through training with the dog. 

In Surrey, UK, police dog puppies start their lives at the dog training center. Then they go to foster homes for the next stage of their training. 

Buying and training a police dog is an expensive undertaking. This puppy, Carl, was purchased by Chief Dan McAfee to work in schools in Sand Springs, Oklahoma. Carl's purchase price and his training will add up to over $8,000.

Even once puppies have become official K9s, their training continues. Dogs are always learning and they often live with their officers. Officers continuously develop their bond with their dogs so that they can work as a team when it counts. 

Police dogs also undergo siren training. As the dogs come to learn that the sirens mean they'll be going for a ride and putting their skills to the test, they start to get excited anytime the sirens go off. These dogs love to work and know their jobs well!