Sci-fi related questions about submarines.

[EFileTahi-A]

Hello, I need some help with ideas and some clarifications regarding possible technologies to be used in sci-fi submarines (using super science if needed). I need this because I'm developing this sci-fi submarine game and it is time to make some serious decisions regarding the technology submarines will use.

1 - Imagine that power output in future would be absurdly high (reaching gigawatts); would be possible to fire powerfull laser beams underwater? Could it, by any chance, be used successfully as a weapon?

2 - Would it be possible to use an energy type of weapon underwater at all?

3 - If I was to develop energy shields how would they operate? How could they work? (I really need a sort of energy shield before detonations or any hazards can reach the subs armor and hull.)

Thank you for any possible information or ideas regarding this peculiar subject.