The traditional models/plans of Turtle always showed a tank and the long, spiral screws for both propulsion and depth adjustment. I wish I could remember just where I found it, but someone evidently found either the original or, at least, an older set of plans and discovered that the screws were bladed, and there was no separate tank.

The US Navy wavered between pull-down screws and dive planes early on, but finally settled on planes. They actually learned how to use them properly by studying German doctrine, originally either linking bow and stern planes, or always keeping the same angle on both, and trying to keep dives on an even keel. (Which had a lot to do with tank design - the early ones weren't subdivided properly, and diving at an angle tended to shift all the water ballast forward or aft.)

J.T. McDaniel