[QUOTE=Marcello;1994075]I have also been told that crew might pick up aircrafts (personally I have never managed when running the periscope watch by myself) via the observation periscope...
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Sorry for the double post but Marcello, I take it from that that if you run with the 'scope up the watch crew automatically do a periscope watch? Which crewman performs the duty, just so I can but my best man on it.

[QUOTE=Gustav Schiebert;1997095]Frankly I do not know, I have just been told here in the forums. On occasion when the noise meter turned red I tried to look for planes on the observation periscope instead of ordering an immediate crash dive, but without much luck so far.Even with the wide field periscope it would be easy to miss the plane until too late. Maybe if I had looked at the map instead I would have seen the triangles for aircrafts as told. But it is not something I feel like experimenting in a campaign.

My understanding is that once underwater submarines usually trim for slight positive buoyancy and use speed to keep themselves down rather than trimming for negative and holding themselves up dynamically. The safety implications of the latter in case of accident are self evident, but I suppose that there might be exceptions, I will try to look into this.
It should not be exceedingly complicated to trim accurately enough for such task. What I would suspect would be more difficult is depth keeping with a stationary boat, as the compensation by pumping would have to be much more frequent.

Let me know what you find and its source. Regardless of the actual procedures, the issue is that the game does not take alternative procedures into account and the boat starts sinking at a certain depth without sufficient speed.