Unlike the previous versions, USAF acquired 112 F-5E/Fs, of which 66 were used for dissimilar training by NATO air forces , due to presenting a maneuverability and radar signature similar to the one of Soviet MiG-21,the Warsaw pact standard fighter of the day. The dissimilar training units were known as " Aggressors " and were based on Nellis AFB in the USA and in RAF Lakenheath, in Britain. In a similar way, US Navy used 10 F-5Es and three F-5Fs for training " Top Gun " at the NAS Miramar jet fighter training center.