The F-35 Lightning II is the result of the Department of Defense's Joint Strike Fighter (JSF) program, which sought to build a multirole fighter optimized for the air-to-ground role with secondary air-to-air capability. The JSF requirement was to meet the needs of the Air Force, Navy, Marine Corps and allies, with improved survivability, precision engagement capability, and reduced life cycle costs. The core engine, canopy, radar, ejection system, subsystems, and avionics are all common among the three different versions.
The conventional takeoff and landing (CTOL) variant includes an internal gun, infrared sensors, and laser designator. This is the technologically simplest version of the JSF, in that it does not require hover or aircraft carrier capability. Therefore it does not require the vertical thrust or the handling qualities for catapult launches, augmented control authority at landing approach speeds and strengthened structure to handle arrested landings.
The distinguishing feature of the F-35B is its short takeoff/vertical landing capability (STOVL). The F-35B variant is designed to operate from austere bases and a range of air-capable ships near front-line combat zones. It can also take off and land conventionally from longer runways on major bases. There will not be an internally mounted machine gun, but an external gun can be fitted. This version requires controllability on all axes while hovering. Another critical design feature is its impact on the ground surface beneath it during hover.
The carrier variant has larger wing and tail control surfaces to enable low-speed approaches to aircraft carriers. Leading edge flaps and foldable wing tip sections account for this increased wing area. The larger wing area also provides the F-35C with an increased payload capability. To support the stresses of carrier landings and catapult launches, the internal structure of this version is strengthened. In addition, the landing gear has longer stroke and higher load capacity, and of course an arresting hook is added. Like the F-35A, the carrier variant will also incorporate an internal gun and sensors.