The identities of all 80 members of the American commando team who thundered into Abbottabad, Pakistan, and killed Osama bin Laden are the subject of intense speculation, but perhaps none more so than the only member with four legs.

Little is known about what may be the nation’s most courageous dog. Even its breed is the subject of great interest, although it was most likely a German shepherd or a Belgian Malinois, military sources say. But its use in the raid reflects the military’s growing dependence on dogs in wars in which improvised explosive devices have caused two-thirds of all casualties. Dogs have proved far better than people or machines at quickly finding bombs.

Gen. David H. Petraeus, commander of United States forces in Afghanistan, said last year that the military needed more dogs. “The capability they bring to the fight cannot be replicated by man or machine,” he said.

Maj. William Roberts, commander of the Defense Department’s Military Working Dog Center at Lackland Air Force Base in Texas, said the dog on the raid could have checked the compound for explosives and even sniffed door handles to see if they were booby-trapped.