Artificial reefs play an important role in leaving larger living spaces for fish, crabs, lobsters, and marine plants. The aim is for these alternative reefs to protect vital offshore installations from storms and erosion while also encouraging marine biodiversity.
During WWII the Germans built wooden airplanes and sometimes complete airfields to keep the Allies away from their real airfields. However, the RAF responded by waiting for them to finish and then dropped a single fake wooden bomb on it.
This is the filter wheel for MIRI, one of the Webb telescope's three imaging cameras. Each of the 18 elements here provides a distinct perspective on the universe.