Historical use and a specific historical example creates a bit of a historical quagmire for a fictional move even when its based on historical events.
Here are some model decals based on historical U-boat art:
(Image removed from quote.)
Various in size and red wasn't shied away from. Honestly, if Allied sailors could make out what is being depicted in the movie at any depth greater than periscope and at any distance greater than point blank range to their own ship, I'd be amazed.
Your patronising BS drives me nuts
Here is a screen shot from the trailer.....
As you can see it covers the WHOLE conning tower.
Using the same "model" info you used...
You can see they had the image only on the upper portion of the conning tower. For a real image....
Again, only on the upper conning tower. Do a google search and you'll find the same for most of the images you can find.
So yes, again, hollywood takes some liberties. But does it change the story? I dont think so. It makes it easier for the "dumb" viewers an easy way to find the "villian".
Stop arguing just for the sake of arguing.