In 1970 Northrop won a competition for an improved International Fighter Aircraft (IFA) to replace the F-5A. The resultant aircraft, initially known as F-5A-21, subsequently became the F-5E. It was lengthened and enlarged, with increased wing area and more sophisticated avionics, initially with an Emerson Electric AN/APQ-153 radar (the F-5A/B had no radar). A two-seat combat-capable trainer, the F-5F had a single M39 cannon in the nose, albeit with a reduced ammunition capacity (the F-5E was equipped with two M39 cannons, one on either side of the nose).
The F-5F was armed with Emerson AN/APQ-157 radar, which is a derivative of the AN/APQ-153 radar, with dual control and display systems to accommodate the two-men crew, and the radar has the same range of AN/APQ-153, around 10 nm. The Swiss F-5F is primarily used for conversion training, control flights and as ECM trainer.
The latest radar upgrade included the Emerson AN/APG-69, which was the successor of AN/APQ-159, incorporating mapping capability, however, most nations chose not to upgrade due to financial reasons, and the radar only saw very limited service in USAF aggressor squadrons and Swiss air force.
At the end of the seventies, the retirement of the Venom and the increased use of the Hunter aircraft for air-to-ground attack caused a gap in the field of air-defence which was to be closed with the Northrop F-5E Tiger II. In 1976 a procurement contract for 72 Tiger fighter aircraft , 66 of the type F-5E (single seater) and 6 of the type F-5F (double seater) was signed. The parts and assemblies were manufactured in the USA, but the Swiss Federal Aircraft Factory, Emmen, carried out the final assembly.
The Tiger were especially well suited for the Swiss "Militia system" and therefore in 1981 it was decided to reinforce the fleet with 38 additional aircraft, of which 6 double seater of the type F-5F.
As the Swiss Tigers have little hours on the airframe, the United States Navy signed a deal wich comprised of the sale of 38 Tigers -to act as Agressors-to be delivered between 2004 and 2007. In 2005 the Swiss Air Force leased 12 Tigers to the Austrian Air Force as a gap filler awaiting the EF2000 deliveries destined for Austria after replacement of the Drakens. All these are returned to Switzerland in 2008.
Under the "future Tiger" project, the Swiss Air Force is seeking a replacement for the F-5s in the next decade. Contenders are the JAS39 Gripen, EF2000 Eurofighter and the French Rafale.