[Krauter]

Lol oh God.. not another Argument Delphin?

First of all: I DO understand the principles of flight (ie: Speed [Velocity is in fact the energy of the aircraft moving forward], Gravity, Drag and Lift..)

Second: As Steve pointed out the Submarine (U-boat if you want to be specific.. A U-boat is in fact a submersible craft thus it belongs to the 'submarine' family of craft..) has pressure on all sides, the same as when an aircraft rises to a higher altitude it loses pressure (and thus air density) out in the atmosphere. How is the Downwards pressure relevant to keeping depth? If you have an upwards pressure that will play an equally important role in maintaining depth (Laws of physics.. Every action has an equal and opposite re-action)

Third: The point of NOT using the pumps is to remain quiet ~ stealthy, invisble <--- the tools of the submarine trade... Thus using speed to maintain depth is inadvisable as it broadcasts your position to anyone listening.