Duct tape was designed during World War I. It was first used to keep water out of ammunition cases. It was found to work so well that people started using it to fix many other things. Duct tape was also called "100 mph tape" by the military because it is said the tape will still stick in winds at speeds of 100 miles per hour. Duct tape got its name from its use on heating and air conditioning ducts but oddly enough, that is the one use that the tape is not very good for. It is illegal in California to use duct tape on ducts and most professional builders in the United States are not allowed to use it either.