The Lockheed Martin F-35 Lightning II is a single-seat, single-engine, all-weather stealth multirole fighter. The “fifth-generation” combat aircraft is designed to perform ground attack and air defense missions. It has three main models: the F-35A conventional takeoff and landing (CTOL) variant, the F-35B short take-off and vertical-landing (STOVL) variant, and the F-35C carrier-based Catapult Assisted Take-Off But Arrested Recovery (CATOBAR) variant. The F-35 descends from the X-35, the winning design of the Joint Strike Fighter (JSF) program. The F-35 first flew on 15 December 2006. The F-35 program is the most expensive military weapons system in history.