SSN-21 Seawolf

SSN-21 Seawolf is a submarine simulator game designed by John W. Ratcliff and published for MS-DOS systems by Electronic Arts in 1994.

The player takes command of a US Seawolf-class submarine and fights in 33 missions with targets under and above water including Russian attack subs, destroyers, missile cruisers, aircraft carriers and frigates. Missions might require the player to defend friendly surface ships from attack, or sink those of the enemy. Other missions have their focus entirely underwater, with the player similarly either defending friendly submarines or hunting enemy missile and attack boats.

Seawolf models the ocean environment, including thermal layers which can be used to deflect enemy sonar and hide the player's submarine. Sonar plays a central role in the game, and the player has access to the submarine's spectrographic 'waterfall' display which is used to detect and classify contacts. Additionally, the game includes marine life, such as whales and schools of fish, that could generate noise or reflect active sonar and create additional contacts.