Hello Blitzkrieg !
Many thanks to have spent so much time to answer my questions. I'm going to read the detailed readme of both H.sie-patch and Stiebler-Addon. Concerning the game difficulty, there is also one thing that i can't bear : when you are submerged and detected by sonar, although the convoy's destroyers didn't know there was a submarine in the area .... I wonder if it has been corrected in a patch ??
And a last question... why this name : Not Your Grand Mother ??