I heard that they trained the dogs to run under the center of tanks (where they could easily fit without getting crushed). They would carry a backpack with a antenna that acted like a trigger when it scraped against the bottom of the tank. In training the dogs would run under the tank and get rewarded for doing so. The theory was the dogs would imprint the idea of running under tanks with a backpack as a sure fire way of getting a treat. Then on their big day the trainers would swap out their training pack for one filed with explosives. Unfortunately they did the training with Russian tanks burning Russian grade gasoline. When the dogs were let out on the battle field they went after what they were trained to run under, things that looked like Russian tanks and smelled like Russian grade gasoline. The results were less than desirable (for the Russians at least).