[Nick Beale]

Look up "butterfly bomb" on Wikipedia and you'll find this: "Butterfly bombs were first used against Ipswich in 1940, but were also dropped on Grimsby and Cleethorpes in June 1943, amongst various other targets in the UK."

I once saw a TV series on bomb disposal and it said that the clean-up in Grimsby had been a massive undertaking because the bombs could hang up on gutters, wires and whatever by their "wings" and not explode. However they were fantastically sensitive, so removing them was a nightmare.