This was very unique! The theme was used greatly and the deep diving gameplay is awesome (you have seen my entry, I might be biased haha), the polish is veeery good and the music is used very well, the sonar ping even fits the tempo. And the tutorial was well implemented, it really helped getting to know the mechanics.
The only "problems" I could find is that the movement might be a little too slow or the level is too big, some parts of the gameplay where just me driving in a straight line waiting to arrive at the location where something happens, perhaps if there where more obstacles, things to explore, collect or with a more compact level design, these moments would not be so noticeable.
Also the combat could have some more elements since a lot of the encounters depended too much on trading damage, maybe things like flares (are they even a thing in submarines?) to reflect missiles, maybe dodging maneuvers and the like could make the combat more dynamic.
These things aren't really problems since the ambiance is very calming and the combat/stealth is still nice, but perhaps some pacing changes could make it more exciting.
Also, it's just a very small thing not really a problem, probably a bug, the rescue bar display stays at zero after the first rescue, but it's not a problem since you can still rescue the crew, only the display does not move.

Overall, this was really cool and the submarine gameplay was very interesting to play, this could definitely serve as a basis for a full game, maybe an arcadey submarine exploration game with stealth/action elements could be awesome, so congrats!
(Sorry for posting a manuscript, the game gave me a lot of ideas lol)