[Alpha Von Burg]

I would agree with HW3, it is unlikly that you hit bottom because your damage was top side.

However, the waters around Scapa Flow are indeed very shallow and it is not possible to dive at a depth of 40m, let a lone beyond 25m.

From your statement, I would say it was a mine because if it were a surface vessel, you would be hearing a lot of pings, because after the fist vessel pings you, more would follow, especially in an area like Scapa Flow.

I would also say that that was a close call, because that mine could have been closer.

Good Hunting...