The storyline of Chromium B.S.U. consists of the player taking the role of a captain aboard a cargo ship. The name of the cargo ship is Chromium B.S.U. The player is given the task of delivering cargo to troops on the front line. The cargo ship has aboard a series of robotic fighter spaceships. Your job is to make use of these ships to ensure that the cargo ship makes it to the front line. Players are expected to shoot enemy aircraft in order to ensure that the enemy aircraft do not reach the bottom of the screen. For every aircraft that reaches the bottom of the screen the player will lose a life. This particular rule makes Chromium B.S.U. unique amongst the usual scrolling space shooters and adds a new degree of difficulty to the genre. Another aspect of the game that makes winning difficult is the lack of ammunition. Ammunition must be utilized efficiently in order to win.