The Boeing F/A-18E/F Super Hornet is a twin-engine 4.5 generation carrier-based multirole fighter aircraft. The F/A-18E single-seat variant and F/A-18F tandem-seat variant are larger and more advanced derivatives of the F/A-18C and D Hornet. The Super Hornet has an internal 20 mm gun and can carry air-to-air missiles and air-to-surface weapons. Additional fuel can be carried with up to five external fuel tanks and the aircraft can be configured as an airborne tanker by adding an external air refueling system.