Oh! let me add this. The sim is wonderfully modeled in that yes you can hold trim (atitude) as you run a few knots at silent running BUT water will still be accumulating in the bilge and you will have to keep your bow planes angling to keep from losing desired depth-station keeping .. or you may have to blow ballast tanks to purge the sea water which is not good as the surface ships look for that. So! be watchful when you go near crush depth because you can lose your boat when the pumps are not working and you have too much sea water accumulating in the bilge weighing you down. If you have a damaged hull, or the worse! You may not be able to get out of it even at full throttle nose up. You will slide back into the abyss and implode.
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DID, no cheats, no shortcuts, no non-historic equipment deviations. Boat and crew safety is integral with my immersion style! Follow the historic events during your patrol:
http://www.uboat.net/today.html