Did you know that Hilbre Island and the Dee estuary were used as decoy sites during WWII?
Apparently the islands and the River Dee were made to look like the Mersey estuary in an attempt to confuse the Luftwaffe into thinking that they were bombing Liverpool. Concrete bunkers on Middle Eye housed diesel generators that generated smoke to give the impression that buildings were on fire and electric lights on poles were positioned in the sands around Hilbre.
For a detailed explanation and interesting pictures of what remains of the bunkers read this forum thread though note that you will need to create a user account to see all the images.