Enter these on the passcode screen:
BUTTERFLY - Unlocks All Missions
TANG - "Bullet Shield" mode
GOBY - Unlimitied Ammunition
MANDARIN - "Achilles Head Mode"
PUFFER - "Always Sniper" mode
BANNER - Invincibility
PARROT - Invisible Soldiers
DOTTYBACK - Men with Hats
TRIGGER - "Invisible Soldiers" mode
HOGFISH - "Perfectionist" mode
DAMSEL - "Rubber Grenades" mode
GARIBALDI - All Replay Items
SPINEFOOT - Makes Everyone's Arms Huge
SEAHORSE - Men With Hats
TILEFISH - Silver Bullet Mode
CARDINAL - Achilles Head
BOXFISH - All Replay Items
WRASSE - Bullet Shield
BETTA - Rubber Grenades
BATFISH - Silver Bullet
JAWFISH - Unlimited Ammo
TUSKFISH - Unlock All Missions
How to find the Trench tool:
The trench tool digs up mud clods for in games secrets. To find the tool you must get to the level named Search of yamashitakas gold and find the lotus flower on a statue inside the palace. Walk up to the front of it and you'll pick it up. As you fall down the hole, go down to the end of the hall into a room with a lying goold buddha statue. There is a pedsetal. Press X on it and it should say YOU HAVE REACHED ENLIGHTENMENT. Then a door will appear to the right and in there is a hammer-like tool.
Dissapearing Soldier:
When doing the 4th mission, Midnight attack on Guadacanal, when the second soldier leaves you and and the other character to ''cover you'' from behind, go in front of him and push him through the level by walking into him. You will have to angle some pushes too. After pushing him a bit, he will vanish and never be seen again, even if you go back to the spot he was originally at.