Galactic Attack

8 Credits from Matt Stelzer
At the title screen (Start/Options), hold L+R+C+Left when you press start to begin the game. You will start with 8 credits instead of 4.

PAR/Gameshark Codes
Master Code
f6000914 c305 b6002800 0000

Player 1 Infinite Lives
160eac30 0003

Player 2 Infinite Lives
160ead30 0003

Level 9 weapon player 1
160eac32 0800

Level 9 weapon player 2
160ead32 0800

Additional PAR/Game Shark codes
Invincibility and level Select - 360DC1Df 7FA1

Go to the options with this code on. Muteki is the invincible code, A+B+C causes you to self destruct.

Level select is the other option.