I learned something new today:

Duct tape was originally manufactured for the U.S. military during World War II by the Johnson & Johnson Permacel division, to prevent water from seeping into ammunition boxes. Because "water rolled off it like a duck" (it was waterproof) and because it was made using "cotton duck" (similar to the material in cloth medical tapes), the new invention was originally called "duck tape." In the booming postwar era, its versatility made it a standard component of any handyman's toolkit; however, its most high-profile use was connecting heating and air conditioning ducts. Thus, "duck tape" became "duct tape." Ironically, the tape is now considered ineffective for ductwork and banned by most building codes.

Wow, that's ironic.