Most Dangerous Weapon in Human History A submarine (or sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.)[2] The term “submarine” is also sometimes used historically or informally to refer to remotely operated vehicles and robots, or to medium-sized or smaller vessels (such as the midget submarine and the wet sub). Submarines are referred to as boats rather than ships regardless of their size.[3] | Life