Here we have the official wwII U-boat diving regulations. It shows (I think) that the alarm bell was only used in crash dive situations. Not when the order came to go to periscope depth. Would be great to have all this in the game but man would it slow it down hahaha.
That being said, it would be euqally great if we could somehow remove the bell sound from the Periscope depth order and move it to crash dive which somehow in my game is silent.
http://www.uboatarchive.net/Diving/DivingRegulations.htm