Dogs take their basic training at Lackland Air Force Base in San Antonio, where they learn to tolerate the crack of gunfire and sputter of helicopters. They are trained to sniff for explosives on command, freezing and staring at suspicious objects.

Merely baring their teeth, they can cow a crowd. Commanded to strike, they can easily flatten a big man with one leap, flying like a 50-pound sand bag tossed from a truck.

Smart and strong Malinois and shepherds predominate, but other breeds are trained too. Even small dogs, like beagles or poodles, are occasionally taught to detect explosives in submarines and other close quarters.

In Iraq, the demand for explosives-finding dogs has escalated. They lead patrols with their handlers in tow, sniffing bags and other suspicious objects along the way.

The bombs have bulked up in past months, putting dogs and handlers at more risk. To protect handlers, some dogs are now trained to wear backpacks with radios and respond to remote voice commands.

"As much as I love these dogs, their job is to take a bullet for me," says trainer Sgt. Douglas Timberlake.

The military estimates spending six months and $25,000 to buy, feed, train and care for the average dog. They are tended by 440 Army veterinarians worldwide.

The dogs get two physical exams each year, more often than most people. They get blood tests, X-rays, and electrocardiograms.

When dogs break teeth with their powerful bites, military vets sometimes do root canals to save the teeth. "Here we treat them, because that's part of that dog's equipment: to use his teeth," says Dr. Lorraine Linn, a dog surgeon at Lackland.

Dogs have been weapons of war since ancient times. Thousands were enlisted in this country's fights in World Wars I and II and in Vietnam. Dogs cannot be awarded medals under military protocol, but commanders sometimes honor them unofficially.

Care for wounded military dogs was more limited in earlier wars. And euthanasia typically awaited at the close of their careers — but that, too, is changing.

Since 2000, a law allows many to be adopted by police departments, former handlers, and others if the dogs are placid enough.

Tech. Sgt. Jamie Dana's German shepherd Rex was plenty friendly but also young and healthy. The military didn't want to let him go.

Rex ended up on an Iraqi roadway when a bomb blew the door off the Humvee he was riding with Dana in June 2005. He suffered little worse than a burned nose and cut foot, but Dana nearly died with collapsed lungs, fractured spine, and brain trauma.

When Rex visited her a couple weeks later at the hospital, she whistled for him and he jumped on her bed. Dana's days as a soldier were over, but she missed her pal.