"Top Secret," part of Secret Access Week on the [National Geographic Channel](http://channel.nationalgeographic.com/ target=), is our effort to get inside the world of black-budget, off-the-books military hardware. Many of you are familiar with Area 51, where top-secret planes are tested. What you may not know is that there's another facility, Plant 42, that's even more interesting, and for the show's premiere, that's where we went. Plant 42 is the manufacturing facility outside Los Angeles, maintained by the U.S. military as a place where private companies can build prototypes under military contract. It's where Lockheed Martin has its skunk works, alongside private facilities for Boeing, Northrop Grumman, and others.