MagnetoHydrodynamic submersible project.
Student project (£100 budget) to build a submersible based around a magnetohydrodynamic drive engine.
The thing about this sort of engine is that it has no moving parts!
It uses the principle that a magnetic field can induce currents in a conductive liquid. Or if you induce a current in a conductive liquid and in the presence of a strong magnetic field, then the liquid can act as the moving part of an electric motor. Moving the liquid in one direction and the vehicle (motor) moves in the other.
Although this was not a huge success (it is not easy to do efficiently) it still did show signs of working.