@ Dan' :

... You're definitely THE man. I've spent some time on google(.fr) searching for "torpedo impacts" and all, but didn't find anything interesting on french sites

. Thanks for your help !
@ Growler : Wow, thank you very much for your explanation. Concerning AP shells, I see what you mean

. It would have been nice to have several deck gun damage textures, one for each type, AP, HE... In case it's possible to mod it, I must say I don't have skills to do it.

Also, the deck gun damage is directly based on the torp damage texture : and none of them (torpedoes) left little holes on hulls.

So even for AP shells, I think you'll never see little holes

. I mean, it's possible to do it, but in case you load the game with that texture, the torp damage will appear as well as a little hole... You see the problem.
Thanks one more time, guys, for your answer !