US patent number 3182517. This Patent appears to fail the usability requirements USA. Note: this is not a software patent.
 Patent Desciption
This invention relates to a method and an apparatus for producing harmonic motion or reciprocation, the amplitude and period of which may be cyclically varied for various purposes related to particular output displacement requirements or variable output force requirements.
The US Patent Office requires that the device be "useful". This device cannot work as described, it is a violation of Newton's Third Law of Motion which states "To every action there is an equal and opposite reaction." The inventor, Norman Lormer Dean, believed that Newton had missed a time element, i.e. that there was a delay between the action and the reaction. This is unsupported by scientific theory. This is Dean's second patent for a space drive, see patent 2886976. The same websites that are devoted to 2886976 apply to this patent as well.
- Dean Space Drive site - Dedicated to the work of Norman Lormer Dean
- Wikipedia Entry on the Dean Drive
- Wikipedia entry on Reactionless Drives
- Jerry Pournelle's story of his involvement with the Dean Drive
 Final Note
This patent, which is for the second Dean Drive is just as notorious as the first patent, 2886976. It also was never legally overturned, despite the scientific impossibility of it's functioning. The arguments made by Norman Dean convinced many people that it actually worked, including Science Fiction Author and Editor John W. Campbell. The reason Dean was able to convince people that it worked, was that when the device was on a surface, that the device, which contained rotating weights, moved. The movement was actually caused by friction between the casing and the surface, as the weights moved, the device moved, and the friction prevented the device from moving back as the weights moved in the other direction. Tests with devices like this which were conducted in vacuum, where friction was not an issue, showed no movement.