In chromium B.S.U. the player takes the role of a cargo ship which needs to bring supplies to the front lines. But he is in danger because of all the evil aliens. Fortunately it has several smaller ships on board which are used to fight the enemies.
The player controls those ships. This game is a classic horizontal shooter: the player can freely move within the automatically scrolling screen. Various enemies approach from above which have to be killed - if they reach the bottom of the screen they attack the player's ship from behind and destroy it. Energy is lost by getting hit from projectiles or touching an enemy but the latter hurts the enemy too. The player can use three weapons (one standard weapon and two special ones with limited ammo) and collect three kinds of power-ups. shield repair, damage repair and a super shield. If the player doesn't collect it he gets other rewards: bonus points (damage/shield repair) or an extra life (super shield). Another tactical possibility is suicide: it destroys all enemies on screen and preserves the ammo for the next fighter.