Why were military dogs Invented?

Protection I believe. They have used dogs for some time now. My grandfather used a dog in WWII to protect himself from Japanese assassins who would kill soldiers while they slept. Dogs having more sensitive hearing would know that an enemy was about before anyone else would realize.

In my opinion Canines have been in the military for a very long time, I have heard other trainers talk about military canines back in Roman times, the uses have changed over the years, but the canine's nose is an invaluable tool.