Duct Tape
The original use was to keep moisture out of the ammunition cases. Because it was waterproof, people referred to the tape as "Duck Tape." Also, the tape was made using cotton duck - similar to what was used in their cloth medical tapes. Military personnel quickly discovered that the tape was very versatile and used it to fix their guns, jeeps, aircraft, etc. After the war, the tape was used in the booming housing industry to connect heating and air conditioning duct work together.