Not having a ballast tank is decidedly NOT a huge design advantage for a military sub, because to stay under the surface you have to keep moving at a certain rate of speed. That is not a desirable trait when your primary goal is to be stealthy.
It IS a great design advantage for non-military subs when your primary goal is to be safe.
The concept is not exactly earth shatteringly new, I've seen concepts of it from navy contractors for decades, the Navy just has no use for one.
For surviving, yes, the only thing can kill a sub is a ship or airplane. How for succesfully completing a mission usually the goal is to remain undetected. That is certainly harder to do.
It IS a great design advantage for non-military subs when your primary goal is to be safe.
The concept is not exactly earth shatteringly new, I've seen concepts of it from navy contractors for decades, the Navy just has no use for one.
For surviving, yes, the only thing can kill a sub is a ship or airplane. How for succesfully completing a mission usually the goal is to remain undetected. That is certainly harder to do.