Well, around 300. Some are out of order, and only a few can still work.
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no
They can submerge, remain submerged and resurface. They are water-tight so that when submerged they do not fill up with water and so lose their buoyancy. Also they have buoyancy tanks into which water is allowed to enter and so increase the mass of the submersible. This makes it submerge. But that water can be pumped out to increase the buoyancy when the submersible wishes to return to the surface.
Infinitely many. Infinitely many. Infinitely many. Infinitely many.
Infinitely many. Infinitely many. Infinitely many. Infinitely many.
so many hours