Hawker Siddeley Harrier as VTOL and STOL manoeuvres (where the traditional lift and control surfaces are useless) requiring skills and technical knowledge usually associated with helicopters. Most services demand great aptitude and extensive training for Harrier pilots, as well as experience in piloting both types of aircraft. Trainee pilots are often drawn from highly experienced and skilled helicopter pilots. In addition to normal flight controls, the Harrier has a lever for controlling the direction of the four vectoring nozzles. It is viewed by senior RAF officers as a significant design success, that to enable and control the aircraft's vertical flight required only a
McDonnell Douglas AV-8B Harrier II to the Lightning II would save $1 billion. After entering service in the mid-2010s, the F-35B will start to replace the AV-8B in 2016, with the AV-8B expected to continue service until 2025. Meanwhile, the AV-8B will receive revamped defensive measures, updated data-link capability and targeting sensors, and improved missiles and rockets, among other enhancements. The AV-8B Harrier II is a subsonic attack aircraft of metal and composite construction that retains the basic layout of the Hawker Siddeley Harrier, with horizontal stabilizers and shoulder-mounted wings featuring prominent anhedral (downward slope). The aircraft is powered by a single Rolls-Royce Pegasus turbofan