688 Attack Sub is a submarine simulator video game designed by John W. Ratcliff and Paul Grace and published in 1989 for MS-DOS and in 1990 for Amiga by Electronic Arts. A Sega Genesis version developed by MicroProse was released in 1991 by Sega.

The player takes command of a US Los Angeles-class or Soviet Alfa-class nuclear-powered attack submarine and plays ten missions ranging from into either Cold War scenarios or combat missions in a hypothetical global conflict. As modeled in the game, the American submarine has more sophisticated electronics and more weapons. The Soviet boat has fewer weapons but higher sustained speeds. Two people can play against each other over a modem (or null modem cable).^{[citation needed]}

Ratcliff and Grace later developed SSN-21 Seawolf, published in 1994.