Enter WL8k Xv57 TwOB WU3C BDA7 cvJ7 2PtH 9EO4 as a password.
Ending
Enter yDaB pc71 jQOA uT3D nfWW 3UKT Yv4g G5WH as a password.
Extra lives
Enter 0000 0000 0000 0000 0000 0000 0000 0000 as a password after completing the game. Defeating a Boss in the next game will result in extra lives.
Hidden ending
Instead of releasing the first P.O.W, select to take a photo, and proceed out of the camp to the pick-up-point. You will be taken back to base. This is a hidden feature. You will be transported back to the first P.O.W when you talk to Commander Murdock. He says you must rescue the P.O.W, and it sends you back.
Invincibility
Enter H800 lbW2 kG4Q KwKc 66WH QbW2 0F1D G19D as a password.
Skip the Flying Fortress
When you reach the final enemy camp, find the POW and rescue him. Then go to the wall and jump into the upper right corner, jiggling the control stick left and right rapidly while hitting the corner. If you are successful, you can go through the wall and back to your helicopter.
Teleport
Stand on one of the "N" and "S" indicators that appear on the ground and press Up.
Turn Commander Murdock into a frog
Defeat the Flying Fortress and proceed to your helicopter back to your base. Go right until you see Commander Murdock running back and forth near the hangar. Fire any weapon at him and a symbol will launch forth, it will turn Commander Murdock into a frog on contact.
Alternate ending, C.O. lives...