N-156F
Single-seat fighter prototype.
Only three aircraft were built.

YF-5A
The three prototypes were given the U.S. Air Force designation YF-5A.
F-5A
Single-seat fighter version of F-5, originally without radar, but was later equipped with AN/APQ-153 radar during upgrades.

F-5A (G)
Single-seat fighter version of the F-5A for the Royal Norwegian Air Force.

XF-5A
Designation was given to one aircraft used for static tests.

A.9
Designation of Spanish Air Force Northrop F-5A which served in the Ejército del Aire.

F-5C Skoshi Tiger
Twelve F-5A Freedom Fighters were tested by the US Air Force for four and a half months in Vietnam.

F-5E Tiger II
Single-seat fighter version with AN/APQ-159 replacing earlier AN/APQ-153 in F-5A.
F-5E Tiger III
Upgraded version of the F-5E in use by the Chilean Air Force, with EL/M-2032 radar replacing the original AN/APQ-159 and capable of firing advanced versions of the Python missile
F-5E/F
A single Swiss Air Force F-5E with F-5F wings.
As of 2011, this aircraft was part of the Museum at Meiringen air base
F-5G
The temporary designation given to the Northrop F-20 Tigershark, equipped with General Electric AN/APG-67 radar.

F-5N
Ex-Swiss Air Force F-5Es used by the U.S. Navy as an "aggressor" aircraft, with AN/APG-69 replacing the original AN/APQ-159.
Intended to replace high-time USN/USMC F-5Es in the adversary role, and see service through to 2015.

F-5S
Upgraded version of the F-5E in use by the Republic of Singapore Air Force, equipped with the Galileo Avionica's FIAR Grifo-F X-band radar and are capable of firing the AIM-120 AMRAAM.

F-5TH Super Tigris
Formerly known as the F-5T Tigris before being officially redesignated.
An upgraded version of the F-5E of Royal Thai Air Force by Israel, It is equipped with EL/M-2032, tactical datalink, Sky Shield jamming pod and are capable of firing the beyond visual range air-to-air Derby (missile).

F-5EM
Upgraded version of the F-5E of Brazilian Air Force equipped with Italian Grifo-F radar.

F-5TIII
Upgraded version of the F-5E, in service with the Royal Moroccan Air Force.

F-5E Tiger 2000
Upgraded version of Taiwan AIDC, equipped with the GD-53 radar, capable of firing the TC-2 Sky Sword II, MIL-STD-1553B Link and GPS/INS.
 Did not enter service as the ROCAF decided to immediately embark on the ultimately-successful process of acquiring additional F-16s to replace the F-5E/Fs altogether.
N-156F
Single-seat fighter prototype. Only three aircraft were built.
YF-5A
The three prototypes were given the U.S. Air Force designation YF-5A.
F-5A
Single-seat fighter version of F-5, originally without radar, but was later equipped with AN/APQ-153 radar during upgrades.
F-5A (G)
Single-seat fighter version of the F-5A for the Royal Norwegian Air Force.
XF-5A
Designation was given to one aircraft used for static tests.
A.9
Designation of Spanish Air Force Northrop F-5A which served in the Ejército del Aire.
F-5C Skoshi Tiger
Twelve F-5A Freedom Fighters were tested by the US Air Force for four and a half months in Vietnam.
F-5E Tiger II
Single-seat fighter version with AN/APQ-159 replacing earlier AN/APQ-153 in F-5A.
F-5E Tiger III
Upgraded version of the F-5E in use by the Chilean Air Force, with EL/M-2032 radar replacing the original AN/APQ-159 and capable of firing advanced versions of the Python missile
F-5E/F
A single Swiss Air Force F-5E with F-5F wings. As of 2011, this aircraft was part of the Museum at Meiringen air base
F-5G
The temporary designation given to the Northrop F-20 Tigershark, equipped with General Electric AN/APG-67 radar.
F-5N
Ex-Swiss Air Force F-5Es used by the U.S. Navy as an "aggressor" aircraft, with AN/APG-69 replacing the original AN/APQ-159. Intended to replace high-time USN/USMC F-5Es in the adversary role, and see service through to 2015.
F-5S
Upgraded version of the F-5E in use by the Republic of Singapore Air Force, equipped with the Galileo Avionica's FIAR Grifo-F X-band radar and are capable of firing the AIM-120 AMRAAM.
F-5TH Super Tigris
Formerly known as the F-5T Tigris before being officially redesignated. An upgraded version of the F-5E of Royal Thai Air Force by Israel, It is equipped with EL/M-2032, tactical datalink, Sky Shield jamming pod and are capable of firing the beyond visual range air-to-air Derby (missile).
F-5EM
Upgraded version of the F-5E of Brazilian Air Force equipped with Italian Grifo-F radar.
F-5TIII
Upgraded version of the F-5E, in service with the Royal Moroccan Air Force.
F-5E Tiger 2000
Upgraded version of Taiwan AIDC, equipped with the GD-53 radar, capable of firing the TC-2 Sky Sword II, MIL-STD-1553B Link and GPS/INS.  Did not enter service as the ROCAF decided to immediately embark on the ultimately-successful process of acquiring additional F-16s to replace the F-5E/Fs altogether.
Northrop F-5