In regards to being able to travel underwater over 500 how many miles per hour I've already revealed how it is done by having a double hull vessel where the outer hole has several holes in it allowing are to escape and a jet propulsion system where is the hole builds up enough pressure with air it would push the air bubbles out and the air would be compressed against the vessel just like a plane flying through the air so with jet propulsion engines it would easily be able to propel itself through the ocean and over 500 miles per hour. A nuclear reactor in a vessel which they already have builds a huge amount of heat when you take water and heated you create oxygen so you have a never-ending supply of oxygen and air to push out through the hull.
Took me about a minute to figure this out years ago. I even drew a sketch of a vessel and how it work. No big deal.