There is no "flying" under water.
The principles are the same and the end result is closer to how aircraft work than to how conventional submarines work.
Penguins look like they fly because they are sleek and elegant - and smol. The penguin also steers by moving forward down and up and not by "drag".
A dozen of one and twelve of another. Flying and swimming both depend on deflecting the medium one is traveling through, which is always going to create drag.
Penguins look like they fly under water because they swim using the same basic principles and control surfaces as flying birds, just adapted to a different fluid.
It's quite pointless to have a sub that can't stay submerged unless it is propelled forward, too. Maybe for a tourist application.
That's like saying aircraft that can't hover are pointless. What would we ever do with aircraft that just fall out of the sky if they stop moving?
There are plenty of things one can do underwater, besides tourism (not that there is anything wrong with sightseeing), that don't require the ability to remain stationary underwater, which would also benefit from the ease of recovery of a positively buoyant craft. Sampling (water, not seafloor) and (sonar) survey work would surely benefit from efficient high-speed underwater travel and the ability to retrieve data that wouldn't be able to be sent from the ocean floor if something were to go wrong. I can also think of at least a few military and supply applications where these would be beneficial features.
About the only things it would rule out would be work on stationary underwater/seafloor locations and espionage or smuggling...and even here there are exceptions. In areas were there are persistent strong currents, craft like these would have an advantage, and if a smuggling vessel is unmanned, or an espionage one lacking in sensitive technology, then the opposing force being able to retrieve it may be a minor setback, but a second chance at recovery for those that deployed it may be a net advantage.
Probably the best way to "fly" under water would be to encase your craft in a supercavitation bubble.
Not as practical for many applications, especially given how it compromises both stealth and one's own sensors.
As for the "flying" sub - the better way to demonstrate lift in water is probably hydrofoils, which eliminate the drag of the body largely by moving it out of the equation.
That's less analogous to
Elite: Dangerous spaceships that--should worlds with dense atmospheres ever become landable--will have to have some way to overcome potentially extreme buoyancy. Wings on our spacecraft make more sense in the DeepFlight-style sense than in the aircraft sense, because to take off from and leave a world all that's required is a thrust to weight ratio of just over one, which any ship with a planetary landing suite has.
Not that I think it's likely any of these shapes are anything other than purely aesthetic, but if they were made to be functional, overcoming buoyancy would be prime pretense for their existence.
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