There is a lot of circumstantial evidence that wherever the intruders came from, at least some died trying. (There were a lot of depth charges fired and moored

There is a lot of circumstantial evidence that wherever the intruders came from, at least some died trying. (There were a lot of depth charges fired and moored mines detonated, sometimes on chance, sometimes as an "exercise", not only in the widely published sub hunts of the era.)