From Cruising Compass: The name: WD40 stands for ‘Water Displacement #40’. The product began from a search for a rust preventative solvent and degreaser to protect missile parts. WD-40 was created in 1953 by three technicians at the San Diego Rocket Chemical Company. Its name comes from the project that was to find a “water displacement” compound. They were successful with the fortieth formulation; thus WD-40