I'm happy that you enjoyed the game! There's a keybind for submarine to dive and submerge (ALT key) or (ALT GR key). I thought about making movement changes softer, tho i faced with the same question some game studios did, realism over fun or vice versa? I still have no clear answer to it but the game would be pretty hard if i soften the movements. It was a tradeoff that i hope not many people feel disappointed with
Thanks for the feedback :D