Based on 1989 Irem coin-op.
N.B. Released on PSX with its predecessor in the compilation "R-TYPES".
Catalogue Entry (French) [Source: Atari Mania]
Pause the game, then hold the LEFT MOUSE BUTTON and ‘F1’, then release both. The screen will turn green, then press ‘P’ to unpause the game. You are now invincible.