The player commands USS Idaho, a fictional Ohio-class ballistic missile submarine, on a routine nuclear deterrence patrol. An encoded message from U.S. COMSUBLANT reports that a stolen Libyan diesel submarine has left the Mediterranean Sea and may be heading into Idaho’s area of operations.

Idaho must evade the potentially hostile submarine, but the situation becomes more difficult because the enemy vessel can use sound-generating equipment to mimic other classes of submarine, including American designs.

The rogue Kilo-class submarine uses this tactic to launch a torpedo attack on Idaho by pretending to be an allied Los Angeles-class submarine, USS Biloxi.