The Republic of Vietnam received 18 F-5Es in 1972, all aircraft being diverted from deliveries originally scheduled for Iran. Other F-5Es followed later. However, it seems that these F-5Es were relatively little used by the South Vietnamese Air Force in actual combat, since their more advanced electronics suite made them more difficult to maintain. Most air action still took place with the earlier F-5A/B model.
During the final North Vietnamese assault on Saigon in 1975, many SVNAF Tiger IIs and earlier F-5A/Bs were flown to refuge in Thailand. A total of 22 Es and four As made it to Thailand. They were returned to the USA and stored at MCClellan AFB, pending sale to other customers. However, most of these ex-VNAF F-5Es remained in the USA to form the nucleus of the aggressor training programs that were started in 1975.
87 F-5As and 27 F-5Es were left behind when the South Vietnamese government fell in 1975. These were pressed into service with the Vietnamese People's Air Force. There are reports that these planes were used by Vietnam during its invasion of neighboring Kampuchea in 1978. In 1979, nine Tigers were reported to be operating from bases near Hanoi as part of a composite squadron also equipped with the MiG-21. The Hanoi unit is believed to have been joined by three other F-5/MiG-21 regiments, marking one of the rare instances in which US and Soviet aircraft operated side-by-side. However, this mix of types caused severe logistical difficulties, and it was decided that the F-5s should be concentrated in just one unit, the 935th Fighter regiment based at Da Nang.
The F-5E/Fs were reportedly more popular with their Vietnamese crews than were the Russian-built aircraft that provided the primary strength of the Vietnamese air force, which is a a rather unique testimonial. They were particularly appreciative of the comfortable cockpits and the ease of handling of the F-5. However, the lack of spare parts and replacements gradually took its toll, and led to a need for cannibalization and to the gradual reduction of the numbers of F-5Es available for service.
A couple of Vietnamese F-5Es (the exact number is uncertain) were sent to Eastern-bloc nations for evaluation. One ex-Vietnamese F-5E arrived in Poland in 1977, where it was disassembled and evaluated. It is now on display at Cracow. Another ex-Vietnamese F-5E (73-0878) made it to Czechoslovakia, and it now resides in the Kbely museum near Prague.
Since the spares problem was becoming more and more acute as time passed, there were several attempts by the Vietnamese government to sell its captured F-5s to other customers. Some were passed along to Iran and Ethiopia as spares. By now, it seems likely that no F-5Es remain flying in Vietnam, the lack of spares probably leading to their grounding, despite cannibalization. Several F-5s are now on display in Vietnamese museums.