In 1942, two years after the Battle of Britain, the question of how to deter or fend off future German attacks on the British Isles remained urgent. How else to account for the Maunsell Forts, a series of structures in the Thames and Mersey estuaries that sat atop pylons and served as platforms for guns to shoot down German warplanes. Some of the forts look like what you’d get if the Walkers from the original Star Wars films tried to walk on water. What is to be done with these forts, which sit in various states of disrepair and were…