A magnetohydrodynamic drive or MHD propulsor is a method for propelling seagoing vessels using only electric and magnetic fields with no moving parts, using magnetohydrodynamics. The working principle involves electrification of the propellant (gas or water) which can then be directed by a magnetic field, pushing the vehicle in the opposite direction. Although some working prototypes exist, MHD drives remain impractical and exist mostly in the world of science fiction. A magnetohydrodynamic drive was featured in the 1990 film The Hunt for Red October, differing from the pump jet propulsion system featured in the Tom Clancy novel The Hunt for Red October upon which the movie was based.
