Re: Is submarine maneuvering harder at extreme depths?

Dear Jim,
	Your question is very interesting and easy to explain too.
As you probably know, water is a non compressible fluid: this means in 
deep sea the density of water is the same you can find on surface.
The pressure, as you have written, increases as much as you go “down”: 
it’s nice to know on the bottom of the Pacific pressure is 16,124 psi.
There is a very simple but also very important law in physic, known as 
Pascal’s principle, stating the value of the fluid pressure acting on the 
different part of a 
body: it’s a constant, in all directions (upward, downward and laterally 
of course...).
So, if you can imagine a tank, you can state the pressure on its bottom is 
the same on the lower part of the walls, regardless its wall are not 
normal to the action of gravity.
Control surfaces of a submarine are “pushed” by pressure in all 
directions and the opposing force, when you move them is zero 
(disregarding the hydrodynamic forces, that are proportional to the 
speed, regardless of pressure). Of course, the structure of these surfaces 
must be strong enough to prevent “implosions” in case of high pressure 
operation, but there aren’t problems in moving them.
I hope to be comprehensible: I’m always ready to explain this better.
Paolo