Submarine Commander Codes -

Level select:
Successfully complete the game.

Powered-up ship and torpedo:
Successfully complete the game, and save. Then, start a new game.

Ghost Ship:
Successfully complete the game two times to unlock the Ghost Ship at the level selection screen.

Unlimited Steel:
Reach the Part 3-7 fight. Talk to the Dock Master and collect 10,000 Steels from her. Save the game, then go to the Dock Master again. She will give you 10,000 Steels again. Repeat to get as much as needed.

To get an unlimited amount of Steel, you must complete or be on at least the second mission. When you get back, the Dock Master will give you Steel. After receiving the Steel, go to the sortie bunker and save at the navigation log. Then, return to the Dock Master and talk to her. You should get the amount of Steel you received previously. Repeat this as many times as desired.

Torpedoes:
Get to the final part of the Part 8-15 fight and get a free Torpedoes at the Torpedo Shop. Collect as many as you can.