Spotting Towers

There used to be hundreds of these things littering the US Atlantic seaboard. With high dollar vacation resort development on the ocean, they're all but gone. In World War II the German U boats heavily patrolled the Atlantic coast looking for convey ships to sink that were supplying the European war effort. These towers were used to spot and triangulate on the U boats when their periscopes popped up. By using simple geometry, two towers spotting the same submarine could inform gun emplacements where to shoot to take out the interloper. These towers are still in place, because this beach is a part of a state park that is protected from commercial development. This region was pretty important to protect at the time because Cape Henlopen is the southern margin of Delaware Bay as it empties into the Atlantic. This is the sea access for Wilmington.