I'm curious about the evidence supporting that it was U-A that was attacked. Veronica Gets Her Tight. This passage seems pretty straightforward: Finally Wolverine ran directly over the sonar contact, dropping a full salvo.

A tremendous explosion lofted water skyward. British sailors reported seeing an orange light below the surface. It was 5:43 AM, March 8, 1941, approximately 60 degrees 47 minutes north, 19 degrees 13 minutes west. That doesn't sound like something that a U-boat survived. And indeed, Prien was never heard from again. The Allies were confident enough to print up and drop leaflets about it to try to embarrass the Kriegsmarine. I'd wager that the ruptured hull of U-47 is on the sea floor, not far from 60°47'N, 19°13'W.