Those textbook answers about using diving tanks to change depth are not the way a sub really works for most of the mission. Yes, the flooding of the main tanks is done to submerge the boat. Once submerged, the boat is put into a state of almost neutral buoyancy and kept there. This is called 'trimming the boat' and it would happen as soon as the boat is submerged, long before it clears the continental shelf.
Some, perhaps most, ship handlers prefer a slightly negative buoyancy. The negative buoyancy proponents like it because the sub handles much like an airplane when it answers to changes in the helm. The downside is that if main propulsion is lost, then the sub eventually sinks down to crush depth. As it is against the regs for a Navy reactor to actually fail, unless its intentionally done as a crew training drill, skippers usually go with the better handling option.
Some ship handlers actually like a slightly positive buoyancy. The positive buoyancy folks trade off better handling against the 'if all else fails, we can always float to the surface' option.
A truly balanced buoyancy is universally avoided. It's almost impossible to maintain depth with that trim and the faster you go, the harder it becomes.
Large changes in depth are done with a combination of the planes and the speed through the water. Certainly not with flooding or blowing the tanks like is often described in literature. Those last two options cause so much acoustic noise that the enemy would hear it half an ocean away and come over to kill your noisy butt.
Boats with sail mounted planes use the sail planes for a fast rise or fast dive at speed and they also use them for small, completely level, changes in depth. This type of boat's rear planes are only used to adjust the angle of attack (or lack of angle) during a rise or dive. Once they are at the new depth or even along the way, small and very quiet changes are made to the trim tanks with pumps to account for the change in water volume in the main tanks as well as changes in water density.
The boats with bow and stern planes can also do a perfectly level change of depth too but it is much trickier to do it in them. They can, however, make a big change of depth faster.
I think that the word 'stall' is not applicable to a sub because there are no lifting surfaces. However, loss of forward momentum will cause a stall-like event to occur. But don't go looking for a flat spin like a Mig 25 gets into with a sub. You've got minutes to hours to contemplate your demise.
Bob
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