Anvart, YOU are the man!
With your hint, I managed to locate the command strings for fully raising and lowering the scopes.
Believe it or not, it is located .cam files. For example:
c:\ubisoft\silenthunteriii\data\Interior\NSS_Uboat 7_CR.cam
It appears I will be able to append a new chunk to each command to play the proper .wav file.
Of course, I'll have to add the new chunk to every .cam file for every turm on every class of boat.
Now, the work begins in earnest. Cross your fingers!