When visitors at Pacific Aviation Museum Pearl Harbor look at the Japanese bomb replicas on our attack wall, they sometimes ask about the little propellers on the bombs. Obviously, these are too small to make the bomb change directions. Some even notice that one of the bombs has two propellers—one on its tip and one at the tail end of the bomb’s body. The answer to the first question is that the propellers are attached to the fuzes that detonate the bomb. The answer to the second is a bit more complicated.
Fuzes have two purposes. The obvious one is to cause the bomb to explode. When the bomb makes impact, the fuze has a spike or electrical circuit that detonates the bomb. If the fuze has a spike, that spike is driven into a small detonation charge that sets off the main bomb charge. An electrical fuze uses a spark to set off the detonation charge. Earlier bombs used pyrotechnic detonation—a flame raced down a detonation line into the detonation charge. Pyrotechnic fuzes were not used in World War II aircraft bombs because of their uncertain detonation time. (In case you were wondering about spelling, pyrotechnic fuses are fuses (with an s), while mechanical or electrical detonators are fuzes (with a z).