Dean was granted two U.S. patents on mechanical devices presumably related to his Dean drive claims. His first patent for a "System for converting rotary motion into unidirectional motion" was granted on May 9, 1959. Another patent for a "Variable oscillator system" was granted on May 11, 1965. These two patent designs were the only ones where Dean revealed the design details with an explanation for operation. However, the details were incomplete, and it is not possible to build a Dean Drive just from the explanations in the patent. Dean's patents, as well as patents for many other similar devices, have been analyzed and it has been determined that none can produce net directional thrust in free space or violate Newton's Third Law. Dean also demonstrated other mechanical devices that were clearly different from his patent designs but apparently never sought patents for them nor otherwise revealed their design details or theory of operation.