That Raymarine unit is a secondary piece of equipment, and is there primarily for its transponder capabilities, which the primary radar unit (the AN/BPS-16, whi

That Raymarine unit is a secondary piece of equipment, and is there primarily for its transponder capabilities, which the primary radar unit (the AN/BPS-16, which I believe is integrated into the masts) probably doesn't have. The last thing a submarine wants is an enhanced "here I am!" capability. Submarines, in general, rely primarily on their passive sensors- passive sonar and EW receivers. A submarine's best offensive and defensive capability is stealth.