Since debuting in 2006, the Lockheed Martin F-35 has become an icon of the United States (US) air power and fighter jet fleet. The F-35s roots trace back to the Common Affordable Lightweight Fighter (CALF) project, later merged into the Joint Strike Fighter (JSF) program in the 1990s. In the end, Boeing and Lockheed Martin presented the X-32 and X-35 concept demonstrators, respectively, for the air forces of several countries to choose a final design.