Phish are already capable of very short turning radius, with applications for monitoring fish, vessels, and equipment.
The GIF, above, demonstrates that Phish can steer in a short turning radius using only the Torque Reaction Engine. By shifting the battery pack a short distance along its driveshaft, Phish will be able to roll between fish and marine mammal orientations, allowing both up-down and left-right steering.Â
In addition, external steering fins can be added and controlled with oil-flooded, depth-capable, low-angle "torquers" (already used in torpedoes), to enable steering like real fish.
More than one TRE, arrayed around the perimeter of a disc, would enable Phish capable of rotating around their central axis, with no preferred direction of travel.