We get at least 2 mines/bombs found off the sea front where I live every year the biggest was not German but a 5000lb British remote controlled anti shipping mine. The idea was guys from the home guard would man the det post 24-7 and if enemy vessels tried to make their way up the Thames he would set it off. It certainly made my house windows rattle when the UXB guys blew it up and that was over 4 miles away. I always wonder why it was not removed straight after the war.
Off the Maplin sands(about 8 miles from me) a few years ago during an exceptional low tide the arse end of a V2 broke surface really wierd to see these tail fins and motor appearing out of the sands they never blew it though as it was not in the shipping lanes so was not threat.
This was the last one found Mine detonation fails