688 Attack Sub is a 1991 submarine simulator game, originally developed by Electronic Arts for MS-DOS computers before being brought to the Sega Mega Drive. It was released alongside M-1 Abrams Battle Tank in the extremely short-lived "Simulator Series" in 1991.
Like, M-1 Abrams Battle Tank, 688 Attack Sub was licensed by Sega of America in 1990, shortly before EA began publishing Sega games for themselves.
The player can control a US Los Angeles-class or Soviet Alfa class nuclear powered attack submarine. There are 10 missions that take place in a Cold War scenario. Players can use the periscope, launch torpedoes, activate sonar to view oncoming submarines or torpedoes, among various other things. As it is a simulator tasks are accomplished by pointing (moving the D-pad; holding will lock it to the next onscreen item in the particular direction) and clicking () with an on-screen cursor. The cursor changes icons to indicate what is currently selected.