Pause the game and press Left Analog-stick Up(2), Left Analog-stick Down(2), Right Analog-stick Left, Right Analog-stick Right, Right Analog-stick Left, Right Analog-stick Right, L3, R3. If you entered the code correctly, you will hear a sound. Damage will be repaired and you will have full missiles. Note: This code can only be enabled one time per mission.
Successfully complete the game, then start another game with your file to begin with all airplanes (including bonus planes), medals, money, stats, FMV sequences, and replay levels that were previously unlocked.
Successfully complete the game and save when prompted. Use that saved game to continue a new game. Successfully complete the Blue Wing Knights mission, then choose another mission. Press Square at the aircraft selection screen to choose from the Vic-Viper and other bonus planes. The Vic Viper has a longer range machine gun that can destroy an enemy plane with one hit. Other bonus planes such as the TwinBee, MX5000, Falsion, Blue Thunder M-450, Manbou-J, Flint-Rock, Aura-Wing, Jerry Mouse, Block Shooter, Super Fighter, Penta, Axelay, and Poly will also be unlocked, depending on how well you performed in your cleared saved game. You can clear the game on the same file repeatedly to unlock more planes.
Focus the game play with Ken. Every time you see Albert, shoot him down. Try shooting him down in every mission. If done correctly, Ellen will be unlocked for the space missions. Ellen has planes such as the Bird Of Prey.
To earn double money, kill enemies using the machine gun (not missiles or bombs). You can use those weapons to damage enemies, but the last hit must be delivered by the machine gun. Some air enemies will give more than double the money. When you finish the mission you will see the scoreboard, showing the enemies you killed with the machine gun with double of the money than normally awarded.
Play an Earth mission with the Vic Viper to hear music from level 4 of Gradius. Play a Space mission with the Vic Viper to hear music from Gradius 2.
While flying the Vic Viper, pause the game and press Up(2), Down(2), Left, Right, Left, Right, X, Circle. The Vic Viper will self-destruct when the game is resumed.