Paul Collins surveys the history of animals for hire. One of the more disturbing examples:
During the Second World War, the Soviet Union resorted to training dogs to wear explosives that would detonate when they ran up to German tanks. It is unclear whether the “anti-tank dog” program succeeded, except perhaps at being horrifying. But that disgust is instructive: animals are killed all the time in war, yet we cringe at sending one to obliterate itself, oblivious to any understanding or possibility of consent. We cannot help but view it as creatures who do understand the motive and causation of a suicide vest.
According to Wikipedia, the Soviet suicide-dog program was extremely ineffective:
In the field, the dogs refused to dive under moving tanks. Some persistent dogs ran near the tanks, waiting for them to stop but were shot in the process. Gunfire from the tanks scared away many of the dogs. They would run back to the trenches and often detonated the charge upon jumping in, killing Soviet soldiers. To prevent that, the returning dogs had to be shot, often by their controllers and this made the trainers unwilling to work with new dogs. …
Out of the first group of 30 dogs, only four managed to detonate their bombs near the German tanks, inflicting an unknown amount of damage. Six exploded upon returning to the Soviet trenches, killing and injuring soldiers. Three dogs were shot by German troops and taken away, despite furious attempts by the Soviets to prevent this, which provided examples of the detonation mechanism to the Germans. A captured German officer later reported that they learned of the anti-tank dog design from the killed animals, and considered the program desperate and inefficient. A German propaganda campaign sought to discredit the Soviet Army, saying that Soviet soldiers refuse to fight and send dogs instead.
One a related note, last fall This American Life featured US military dogs on the front-lines of WWII.
(Video: What appears to be a Soviet propaganda film about the anti-tank dogs)