Submarines

The ability to stay hidden deep under the waves makes the submarine a powerful and effective warship. To travel underwater, a submarine needs a strong hull to resist high water pressure, and engines for both surface and underwater use. Submarine were used effectively as deadly weapons for the first time in world war 1.Today there are two main types of military submarines in operation. A patrol submarine searches for and atttacks enemy vessels. A missile submarine carries long-range nuclear missiles

the most powerful submarines are those that carry nuclear missiles, and are driven by nuclear engines.Each missile can destroy a large city, killing thousands of people.
Nuclear engine allow a submarine to stay submerged for much longer than other submarines, which have to return to the surface to recharge thier batteries.