In 1942, Winston Churchill ordered chemical and weapons testing facility Porton Down to find a way to weaponize anthrax against the Nazis. One of the plans they came up with would have killed in such an indiscriminate manner that it would have more than lived up to its sinister name of... "Operation Vegetarian".
Anthrax is an infectious disease caused by the bacteria Bacillus anthracis. Depending on how animals (or humans) come into contact with the bacteria, anthrax ranges from deadly to "just take this guy to the morgue". When inhaled, the fatality rate is higher, but when ingested (and treated) the survival rate is now still only 60 percent, even lower during World War II. What's more, it spread effectively and indiscriminately between animals.
Operation Vegetarian was as simple as it was ludicrous: The British would launch cakes at the enemy. Well, specifically "cattle cakes" for cows. The idea was that Royal Air Force bombers would drop anthrax-laced cattle cakes onto fields where cattle were grazing. The cows would eat up the cakes, unknowingly infecting themselves with anthrax.
The cows would then either: 1) die, 2) infect others and then die, or 3) infect humans and then die. While bad for the cows, you've probably guessed that they weren't the main target. The goal was to wipe out the food supply and cause humans to eat infected meat, where the bacteria would hopefully spread between people and essentially starve the enemy. As a bonus, they figured that Germany may stay away from meat altogether (hence the name "Project Vegetarian"), crushing their morale.
Of course, one of the main problems with the idea is how indiscriminate anthrax is. Essentially, the plan could feasibly have killed millions of people, civilians and Nazis alike.
However, that wasn't what got the project canceled.
In 1942, the British attempted to test the project by attacking sheep on Gruinard Island, just off the coast of Scotland. A flock of sheep was placed near an explosive device, surrounded by anthrax cakes, the preferred delivery method of the attack.
The sheep all died within a few days, while anthrax contaminated pretty much the whole island, making it necessary to quarantine the whole place. The sheep were buried – but one managed to become unearthed and drift across the sea to mainland Scotland. The corpse was partly eaten by a dog, who went on to cause an outbreak amongst local livestock and pets. The incident didn't put the British off the plan entirely, but by the time they were ready to implement it, the Nazis were on the retreat, making the whole plan unnecessary.
The island continued to be contaminated with anthrax until around 1990. The only victims were a whole load of animals, all of whom were British.