A quick look in the Silent Hunter 4 Downloads section, under Missions and Maps, and there is
http://www.subsim.com/radioroom/down...o=file&id=4053
on the first page... Just a couple mouse clicks away...
haven't a clue myself about the Walter's, but someone else (you??) were told that you had to end the mission in order to get it charged.
http://www.subsim.com/radioroom/showthread.php?t=229366