usarmy973

If you had a time machine, what time would you go to? The future, the past? What would you do once you got there?

Let me add to that... (former submariner here). Subs have an inner hull and an outer hull. The inner hull keeps the people in. Between these two hulls we have ballast tanks. When the sub is on the surface the ballast tanks are full of air. We are very buoyant. When we want to sink, we let the air out and let them fill with water. We then try to achieve neutral buoyancy. We use what's called trim tanks to modify the overall weight to get neutral buoyancy. Once we have it, we use the propulsion to move forward, and the control surfaces move much like the wings on a plane. Instead of using aerodynamics like a plane does, we use hydrodynamics. That's how we move up and down and left and right.

What he said about sonar is right...but... he's talking about active sonar. There is active sonar (ping, ping) that we can use to "see" underwater. And there is passive sonar where we just listen.

For navigation we primarily use GPS when we are on the surface, and then keep track of where we are going and computers figure accordingly once we are deep.