Skunk Works is an official alias for Lockheed Martin's Advanced Development Programs (ADP), formerly called Lockheed Advanced Development Projects. Skunk Works is responsible for a number of famous aircraft designs, including the U-2, the Lockheed SR-71 Blackbird, the Lockheed F-117 Nighthawk, and the Lockheed Martin F-22 Raptor. Currently its main, largest officially known project is the Lockheed Martin F-35 Lightning II, which will be used in the air forces of several countries. Production is expected to last for up to four decades.