The third Swift variant was the "F Mk 3", with 25 being built and powered by an Avon 114 engine with reheat. It was never taken into operational service with the Royal Air Force and was used as an instructional airframe. The next variant was the "F Mk.4", which included a variable incidence tailplane intended to correct the handling problems that the Swift suffered from. It did indeed fix the problem; however, it was found that reheat could not be ignited at high altitude which added to the Swift's list of problems.