Historic England have released the "Aerial Archaeology Mapping Explorer" which is a must see, it is not complete
but has an amazing amount of detail about WW2 structures on the Wirral.
As well as some medieval sites it has:-
Barrage balloon sites
Public street air raid shelters
Public park air raid shelters
I can't find a direct link to the map, you have to go through this page to avoid a login script and to pick up a session id. About half way down is "explore the map" in a box.