In World War 2 US created a bomb that used bats. The bats would be carrying small incendiary charges and would be released from the bomb in mid air, causing them to fly and scatter to different buildings in the area. The charges would then detonate and set all the buildings on fire. It was tested and proven to be very effective.

This was actually APPROVED by the government for development and production, and then cancelled because of the atomic bomb. The idea was thought up by a Dentist who was friends with Eleanor Roosevelt.