I just had a very successful first run into Scapa Flow. I killed a fleet carrier and an auxillery cruiser.
I took the western most approach, and then went to the south of the island in the inlet. Only one PT boat stood in my way. No sub nets or mines and once in I could see all the destroyers cruising around to the southern and the eastern approaches (whahahaha, fools!) I stayed submerged for the entire trip so I don't know about shore batteries.
Here're some photos.

No escape now!

I didn't really get the timing of this correct. It was an amazing explosion.
I fired 4 torps at the carrier however the first one destroyed it instantly.
Hope you have the same luck as I did!
M
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CANNABIS COLLECTIVE