Harpoon II, from Intracorp is the most realistic submarine simulation game you can play without needing a security clearance. It uses the same sort of radar signals and codes as one would find on a real submarine, though the game is played in tactical mode.

Harpoon II comes with 15 scenarios and 8 tutorial scenarios that teach you how to use the various controls, how to dive and surface, how to use the weapons, and other things you will need to know during play.

Each of the scenarios comes with a briefing covering your objectives during the mission. The scenarios cover most of the world's oceans, from the Pacific to the Atlantic and back. ~ Lisa Karen Savignano, All Game Guide