Ok I'll add some more
-U-boats were possibly considered holy by the Kriegsmarine ships,because they would not hesitate to beach themselves just to get out of the U-boat's way;
-When the crew-men died,they are instantly taken to heaven or hell;
-When a compartment filled up with water,everyone in the sub would immediatly perrish and the sub would be destroyed;
-Some towns enjoy water so much,they are build so that when tide comes in or there's a big storm,about half of the town is under-water;
-The navy fanfare was fed with "Uber-soldat" pills so that they could sing for days on end untill the U-boat came back in port.Either that or they used telephaty to tell when the U-boat would come back;
-About 99% of people in the U-boat roster had blonde hair and blue eyes ;
-Highly advanced tech allowed the Radio-operator to turn on the gramphone with his mind;
-On some small subs,the Hydrophone could not be manually turned by touching the wheel,but could be turned by touching the dial-display;
-In order to alert the Command-room crew of damage to another part of the ship,a very advanced sensor made a pipe explode in the command room whenever there was slight damage to another part of the sub;
-Lights were so powerfull that they could pass through almost everything;
-The crew on all other ships looks alike,no matter what country they are from;
Will be adding more as I remember them
Edit:Just remembered some more
-Elco's and other similar water-craft carried torpedoes just for show,since they were never used;
-Light machine-guns ,such as the ones mounted on torpedo-boats could potentially cause heavy flooding to a surfaced u-boat;
-Tug boats were again made just for show,they did not help subs that were out of fuel or other ships that were downed;
-very light AA guns on early u-boats could be used to completely destroy heavy cannons on BB's;
-If dc's were dropped on a submarine that was going at periscope depth ,they would pass straight through the submarine and cause no damage whatsoever;