Back in the 40s, during the war, the Lockheed Air Terminal in Burbank was a massive facility that produced warplanes from the P-38 to the B-17 bomber.
Located in a city on the west coast, however, it was considered vulnerable to Japanese bombers. Rather than moving the facility, Lockheed took what some might consider an even more drastic step: they hid it in plain sight. This is a picture of the same facility taken from more or less the same angle as the picture above:
What had been runways and production buildings and terminals and massive parking lots now looked, from above, like nothing more than an ex-urban subdivision of houses set alongside rolling fields of alfalfa. A perfect trompe l'oeil.
Below the "fields," business went on as usual:
The main Lockheed plant and runways were made to appear as grain fields and houses, and the parking lot was covered over with netting to appear as alfalfa fields. In addition, an extensive smoke screen system was installed to hide the plant under smoke.
Nowadays I'm sure we'd have some kind of super-complex satellite-based missile defense shield or something -- but I think this goes to show that sometimes, simpler is better.
[via Think or Thwim]