In 1979, the government of Singapore ordered 18 F-5Es and three F-5Fs, along with a batch of AIM-9 Sidewinder air-to-air missiles. The arrival of these planes enabled Singapore's aging Hawker Hunters to be transferred to the ground attack role. Between 1981 and 1983, six more F-5Es and three more F-5Fs were delivered, and a batch of AGM-65A Maverick missiles were ordered. A second squadron was formed in June 1986 and six more F-5Es were acquired to equip it. In December 1987, three more F-5Fs were delivered. The final Singapore Tiger II order was for a batch of five F-5Es which were delivered between January and August 1989. Although the Northrop F-5 production line has already closed down by that time, these last aircraft were assembled from its spares stock. In fact, Singapore was the recipient of the last F-5E built, which bore the USAF serial number 86-0409 and the SAF serial 874
In 1991, Singapore Tiger IIs were scheduled for a major upgrade. This upgrade included the installation of such things as a new avionics fit of HUD/WAC, Elisra SPS-2000 radar warning receiver, Litton LN-93 laser INS, GEC-Marconi HUD, two head-down color, MFDs, HOTAS controls and a new air data controller, all supported by a MID STD 155B databus. Perhaps the most significant change is the replacement of the original equipment Emerson radar fire control system with the FIAR Grifo F/X Plus multimode pulse-Doppler fire control radar (as fitted to the AMX). This radar has 10 air-to-air and 14 air-to-surface modes and is compatible with the AMRAAM and SARH missiles. In order to accommodate the new radar, a nose plug has to be fitted which pushes back the forward bulkhead, and one of the two 20-mm cannon needed to be removed to fit in the larger antenna. In March of 1996, Singapore Technologies Aerospace announced that it had been given a contract to carry out the upgrade, with Elbit of Israel being an important associate. These aircraft were redesignated F-5S/T respectively after refurbishment. Two upgraded prototypes had been test flying since 1994 but have had problems with integration by Elbit of Israel of the FIAR Grifo F fire control radar
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By end of 2009, the type had accumulated more than 170,000 hours of flight time in Singapore service with only two F-5Es being lost in separate accidents (in 1984 and 1991, respectively). As of June 2011, only 141 and 144 Squadron are left operating the RF-5S and F-5S/T, as 149 Squadron formally transitioned to the McDonnell Douglas F-15SG Strike Eagle on 5 April 2010