Since your just starting out, I suggest you ignore the mission, go sink 60 to 100 thousand tons (refit as necessary), go back to port, end patrol.
I have done this mission, it is a very sticky situation. Not a lot of places to surface, recharge or save games.
PS: other threads talk about problems saving game submerged with too many contacts nearby. restarting from those saved games is sometimes very iffy.
welcome aboard, and happy hunting.
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