Hello mark1939 and welcome to the subsim forums
There is a problem with enemy subs in the stock game lead to ctd.
There is a
fix for this. Download the
Jonesoft Generic Mod Enabler, extract with
7zip and copy jsgme.exe and the other files to your game folder (where the sh5.exe is located). Run jsgme.exe, a folder called MODS will be created. Extract the fix to the MODS folder (MODS/fixname/data). Enable the fix using jsgme.exe. Maybe this will help with your issue.