 The F-35B STOVL variant of the Joint Strike Fighter (JSF) aircraft is intended to replace the vertical flight Harrier, which was the world's first operational short-takeoff / vertical-landing fighter.A requirement of the JSF is that it can attain supersonic flight, and a suitable vertical lift system that would not compromise this capability was needed for the STOVL variant.The solution came in the form of the Rolls-Royce LiftSystem, developed through a $1.3 billion System Development and Demonstration (SDD) contract from Pratt & Whitney.