A police dog's most valuable tool isn't his bite. It's his nose. Studies show that a German shepherd's sense of smell is 1,000 times stronger than yours and mine. And those noses are one of the most potent weapons police have in the war on drugs – and terrorism.

At the Philadelphia Police Department, intensive training goes into producing a sniffer dog. For example, it takes 14 weeks of patrol training for a dog to learn the basics, like tracking and apprehending criminal suspects. Another 2 1/2 months of cross-training in either explosives or narcotics detection will turn a German shepherd's nose into a virtual radar detector for all that is mind-altering or combustible on the streets. The department's Labrador retriever is also trained, exclusively, in scent work.

The Bomb Sniffer

In the parking lot behind the department's canine unit headquarters, trainer Steve Withers is working with Buddy, a willowy shepherd whose airy gait wouldn't wake baby. "Find the bomb," Withers says, running his hand over the back tires of a blue Toyota in a "directed search."

Buddy sniffs tenaciously, his nose trailing his master's hand. When he reaches the front of the car he immediately goes down on his haunches. No wild yelping or leaping about. He just sits. Withers praises him and tosses him his soiled "end article," a filthy white towel that's twisted up and bound in tape. To a police dog, the end article – used as a reward when he does the right thing – is as welcome as a favorite blanket is to a child.

Reaching into the car and pulling out a pipe bomb, Withers explains that explosives dogs must be docile and that they're trained to give a "passive indication" - sitting down, as Buddy does - when they smell a bomb. You can't have an excitable dog jumping around once he's located the explosives.

The unit trains its bomb dogs on 21 different types of explosives. The common ingredient that the dogs hone in on is nitrates, also present in many household items, like shoe polish, fertilizers and VCR tapes. Withers says police handlers are taught to discern weak from strong indications, which most dogs will only elicit if explosives are present.

Nevertheless, there's no avoiding the occasional confusion. When, for example, the department conducted bomb sweeps at Independence Hall in preparation for a presidential visit in 1984, the dogs repeatedly indicated a bomb in the pantry area of a Secret Service lounge. The puzzled officers - finding no bombs - finally realized it was the bottles of nitrate-laden Coca-Cola under the sink that had sparked the dogs' responses.

Those dogs weren't wrong: When they're using their noses, they rarely are. In the wake of a terrorist scare a few years ago, a company tried to sell the City of Philadelphia a new type of bomb detector. When officers tested the machine against a dog, the machine's sensor flagged two out of five bombs. The dog, on the other hand, found all five.

Training the Dog Behind the Nose

Scent training, explains Officer Paul Bryant, head trainer at the canine unit, starts with white towels. The handler and dog play with the towel. Then, the handler hides the towel for the dog to find. Eventually, the towel is sprinkled with black powder - for explosives training - or wrapped around pouches of marijuana - for drug detection. The trainers, who have Drug Enforcement Agency (DEA) licenses, plant more potent drugs - cocaine, crack, heroin and methamphetamine - in closed containers. When the dog picks up the scent of, say, heroin, he's egged on.

"You've just imprinted his olfactory sense with heroin," Bryant explains. A couple of years ago, Bryant's dog, Azeem, a longhaired, black-and-tan shepherd with strong German lines, became Philadelphia's first dog trained to find dead bodies, one of an exclusive group nationwide that specializes in the job. These dogs can sniff out tissue that's 6 months old, bones that have been buried for 2 years and body parts that are underwater.

Says Bryant of the work he does with Azeem: "I do it for closure. If I can help one family say good-bye to someone, if I can do that for one family..." he trails off. Yes, he admits, it's gruesome. But the payoff makes it all worthwhile.

The dogs, on the other hand, don't understand the nature of their searches. Rather, they relish their olfactory mission as though it were a game. And in a sense, it is. Because of the dogs' powerful noses and stalwart obedience, it's a game society wins.