City Under Siege was based on the arcade game Cyber Police ESWAT released a year earlier in 1989. The console game maintains the main characters, plot and some of its enemies from the arcade game, but features some different levels, weapons, and bonuses. The game was later re-released for the Wii Virtual Console in Japan and PAL regions and included in the Sega Genesis Classics internationally.
ESWAT is a run'n gun type of game, on which the player must eliminate threats approaching from either part of the screen; a boss is waiting at the end of each stage. After completing the second mission, you are given a power suit and weapons.
A police officer (named Duke Oda in Japanese versions) navigates through the crime-ridden Liberty City, shooting and capturing criminals. He is eventually accepted to the Police Department's top unit, E-SWAT (Enhanced Special Weapons and Tactics) and given a powered exoskeleton to fight against powerful crime bosses who threaten the city. His ultimate goal is to destroy E.Y.E., a super computer.