688 Attack Sub is a submarine simulation game developed by SEGA for the Sega Mega Drive, bringing a technically ambitious naval warfare experience to a console platform more commonly associated with fast-paced action titles. The game places the player in command of a Los Angeles-class nuclear attack submarine — the USS 688 — and tasks them with completing a series of Cold War-era naval missions across hostile ocean environments. The title arrived during a period when the Mega Drive was establishing itself as a platform capable of hosting complex, adult-oriented games beyond the arcade-style fare that dominated its early library, and 688 Attack Sub stood as a notable example of that ambition.
Gameplay is built around the management of submarine systems rather than twitch reflexes. Players must balance sonar monitoring, torpedo tube loading, periscope observation, and navigation simultaneously, creating a layered experience that demands patience and strategic thinking. The control scheme maps these subsystems across multiple screens or panels, and players switch between views — including the sonar waterfall display, the navigation chart, and the weapons console — to gather information and execute attacks. Enemy vessels, including surface ships and opposing submarines, must be tracked using passive and active sonar before a firing solution can be established, and premature use of active sonar risks alerting adversaries to the player's position.
Mission objectives vary across the campaign, encompassing tasks such as intercepting enemy convoys, evading hunter-killer submarines, and striking high-value surface targets. Depth management is a constant tactical consideration: diving deep reduces the player's acoustic signature but limits weapon deployment options, while operating at periscope depth allows for visual confirmation and communication but exposes the boat to detection. Damage management adds further tension, as hull breaches or flooded compartments must be addressed before they cascade into a fatal loss of pressure integrity.
The Mega Drive version adapted what was originally a PC simulation title, and the conversion brought the core systems to console with controls reworked for a gamepad. While some of the granular detail present in the PC original was streamlined for the platform, the essential simulation loop remained intact. The game earned respect among players who sought a more cerebral challenge on the Mega Drive, distinguishing itself from the platform's dominant genres of platformers and beat-em-ups. Its presentation leaned into functional, information-dense displays rather than visual spectacle, which suited the subject matter but required players to invest time learning the interface before the strategic depth became fully accessible.
