Blue Marine Zone is the fourth zone in Sonic Blast, consisting of underwater ruins. It follows Red Volcano Zone and precedes Silver Castle Zone. This is one of only two Zones in the game to have water, the other being Green Hill Zone.
Mostly following the same rules as other water-based Zones, the player must inhale air bubbles to prevent from drowning, but if there are none nearby, then Sonic/Knuckles can jump into a pipe for the same effect. There are also invisible water currents in this stage which should be avoided, as they will pull the character to different areas.
This battle is fought entirely underwater. Robotnik attacks the player in an egg-shaped Submarine that can fire harpoons aimed at the player from an underside-mounted launcher.
If the harpoons strike the ground, they produce a single air bubble - this is the only form of oxygen available during the fight, so the player must be sure to take advantage of it. The submarine's cockpit is its weak point, which must be hit eight times to destroy it.