[Abd_von_Mumit]

Originally Posted by DS

I believe there is a RL difference between "operationally" surfaced, and surfaced with all tanks blown dry.

Operationally, I believe that some ballast tanks were kept flooded for safety reasons (call it reserve potential bouyancy), and the boat sat lower in the water, which is what we see with most photos.

With all tanks blown dry, the boat would obviously sit higher in the water, be less stable (pitch and roll), and may have better speed/efficiency characteristics as less hull in the water means less drag.

Sub experts please feel free to correct the above.

Giving the first post here, it seems this is moddeled by SH3, which is cool.

1. I've performed tests of speed and diving time for "surfaced" and for "depth 0 meters" - no difference in performance at all. More on that in post #3 here:
http://www.subsim.com/radioroom/showthread.php?t=129286

2. From Kriegsmarine "Submarine Commander Handbook":

29.) The danger of a surprise attack exists, in particular, when the submarine comes to the surface, especially after traveling long distances at considerable depth. When coming up from a considerable depth, an all-round sound location should therefore be carried out at a safe depth, where the submarine cannot be rammed; i.e., at a depth of approximately 20 m, at "sound-location speed." Next, the submarine should go rapidly through the danger zone at periscope depth, with the periscope raised; careful all-round look-out with and without magnification - submersion up to 9 m, depending on the weather, then lower the periscope altogether (see No. 23) and surface at high speed. The manhole of the conning tower is opened as quickly as possible, and the commander - with, at the most, one man who is especially good as a look-out - goes up. It is not until the surface of the sea has again been examined with binoculars, in every direction, that the compressed air cells can be completely emptied of water.

The bolded sentence firmly suggests, that surfacing for a longer time always meant full emptying of tanks.