Submarine warfare systems are in a class of their own. You may have seen the 1990 espionage thriller movie The Hunt for Red October. It portrays a late Cold War era encounter of various submarines. Suffice to say, a real suspense flick.
In WWI, German U-boats (submarines) were highly successful in sinking ships of foreign navies and merchant vessels. Initially the sudden loss of those vessels was unexplained but the then novel submarine warfare technology was quickly recognized and countered with other technology.
