Tunnel B1 Codes -

All weapons and full life (PAL version):
Press L1 + R1 + L2 + R2 + Square + Circle + X + Triangle.

Level skip (PAL version):
During game play, press Start to pause. Highlight "Continue" and press Select.

Unlimited weapons:
Successfully complete the game and save the data with the yellow "Orpheus" text. Load that saved game to restart with all weapons and unlimited ammunition.