Extra continues:
When all your continues are used up and your last sub has just been destroyed, press and hold Triangle and Select. Then, with these buttons held down, press Start. You will get 5 more continues.

Level select / Two-player battle mode:
Go to the title screen and with the cursor on Start, press: Up/Left + O + Select. The stages will now appear at the top of the screen. Press Right or Left to scroll through the choices. Press Start to choose the desired stage. One of the more interesting level is a two-player Battle mode.

Avoid death:
In the one-player mode, when you are about to die, press Start on controllertow to pick up the game where you left off, now in controller of the Player Two submarine.

Speed up:
Pause during a game. Hold Triangle + R2 and resume the game.

Slow down:
Pause during a game. Hold Triangle + L2 and resume the game