MAGNETIC SUBMARINE

* Build a wide, flexibe, hollow tube of strong waterproof material 
(maybe reinforced with steel mesh), with magnetic elements embedded 
within it.

* In the centre, place electromagnets designed to programmatically 
attract or repell the flexible "hull" of the submersible. By always 
predominately pushing outwards from the center, the magnets provide 
the missing compressive strength required to maintain a void inside 
the craft.

* Changing the overall magnetic field changes the shape of the hull 
- the submersible can bend its "body" to swim like a fish, eel, 
etc. Without any mechanical moving parts!

* Very tiny submersibles may be more practical to make due to less 
distance that the magnetic field has to extend over between the 
centre and the hull at maximum repulsion.

* The electromagnet (unless using some clever method of 
electrically modifying the field of powerful parmanent magnets) 
would probably require more power than could be supplied onboard 
the craft, eg. batteries. So you could connect a cable to a 
floating platform on the surface of the water that supplies power 
(and also maybe control, switching etc.).

RELATED THOUGHT:
* Back to my ideas for vacuum airships, which I never finished 
writing about here, would it be possible for the magnet to be light 
enough that the same principle could be applied to create a buoyant 
vacuum balloon in air? Maybe with specially engineered permanent 
magnets like these?
http://www.polymagnet.com/

 - The Free Thinker, 2020.