Submarines today are highly complex machines crammed with technology and weapons. As impressive as their construction is, as terrifying is their destructive power. Hardly any other weapon triggers as many emotions as the submarine. It strikes from ambush and can use nuclear missiles to drag the whole world into the abyss.
Submarines originated from a completely non-military idea, namely to be able to view the world under water. But the interest in the military use of submarines soon prevailed.