Designed from the start as a low-weight, low-cost fighter the Northrop F-5 became an export success. It is also a very recognisable fighter aircraft. Typical is the shape of the fuselage: when viewed from the side the bottom is nearly flat, while the top is curved from the nose over the canopy to the exhausts. At the back, the canopy is flush with the top of the fuselage. The wings are thin and flush with the bottom of the fuselage. The air intakes have about a D shape and are below the canopy. Another key feature is the trapezium vertical stabiliser with forward swept trailing edge. Finally, the two side-by-side external exhaust pipes at the very end complete the appearance of the F-5.

The single seat version of the F-5 was developed into the single engine F-20 Tigershark. A dedicated supersonic trainer was based on the N-156T, designated T-38 Talon.

Iran developed its own versions of the F-5, of which most look externally hardly different. The exception is the Saeqeh (see Confusion possible with).

The different versions of the Northrop F-5, F-20 and T-38 can be distinguished by looking at:

• the shape and length of the nose
• the presence and shape of leading edge root extensions on the wings
• the number of engines
• the size and shape of the air intakes
• the presence of (fixed) tip tanks
• the shape of the canopy
• the presence of a triangular dorsal fin
• the shape of the middle side of the fuselage
• the location of the (removable) tank boom
• the presence and number of cannons in the top of the nose
• the shape of the landing gear
• the shape of the speed brakes
• the presence of leading edge flaps
• the shape of the exhaust(s)

It all started with a set of concept designs, of which model N-156F was the only single seater to be built. It was eventually developed in the YF-5A with stronger wings and gear. Both already possess most of the F-5 basic features described above, and of the F-5A variants below. These include small triangular leading edge root extensions of the wings, and the well visible curve line between the spine and the fuselage side, behind the canopy and above the air intake. Also, they have two rectangular speed brakes in front of the main gear, placed next to each other. Typical for the N-156F and YF-5A specifically is the lack of two cannons in the top of the nose. The wing tips can be with and without missile rails, but rarely have tip tanks. They also initially had a large instrumentation boom sticking from the nose.

The production version is the F-5A, with popular name Freedom Fighter. Compared to the YF‑5A it has two cannons in the nose, in front of the canopy. Moreover, they normally have tip tanks with a 'wasp waist', i.e. their diameter is smaller in the middle than towards the front and end. Missile rails can also be fitted though.

F-5A(G) is the designation for the Norwegian air force variant with heated wind screens, an arrestor hook (hardly visible) and provisions for JATO rockets (not always fitted).

The Spanish acquired their first F-5As from the Canadian production line, but externally these SF-5As are the same as the US-built F-5As.

The Canadian government arranged license production for the F-5 as part of the order. These CF-5As are slightly different from the US built airplanes. Most important is the engine variant that needs more air during slow forward speed. This air comes through six louvre doors in the side of the fuselage, just behind the wings. When the extra air is not needed, these doors are closed. Also, the CF-5A can be equipped with a fixed refuelling probe on the right side, below and in front of the canopy. Finally, the nose can be quickly changed for one with cameras instead of cannons. These are known as CF-5A(R).

In Canadian service, the CF-5A was called CF-116, while versions for the Netherlands and Venezuela are designated NF-5A and VF-5A respectively.

The photo reconnaissance version of the F‑5A is designated RF-5A. Its nose has several windows behind which cameras are placed. Both cannons remain in place. The nose shape is not really different from that of the regular F-5A, except for the tip below the pitot tube, which has a forward looking camera. It is certainly not as modified as that of the TigerEye.

RF-5A(G) and SRF-5A are the model desig­nations for the Norwegian and Spanish variant respectively.

Although Northrop had already developed a dedicated jet trainer from the N-156T, the T‑38 Talon described below, there was still a need to a training version of the F-5. This became the F-5B. It is basically an F-5A with the front fuselage of the T-38, with its typical slightly turned up nose with pitot tube on top, and without cannons. Of course it has a longer canopy, that opens in two parts. For the rest it has the charac­teristics of the F-5A, like the fuselage spine curvature, triangular leading edge exten­sions and tip tanks. 

These are the two seater versions of the Canadian built F-5s. They have the same nose as the F-5B, but also the louvre door air intakes typical for the CF-5s. In Canadian military service they are known as CF-116D.

Turkish NF-5Bs were upgraded with head-up displays (HUD) and after that called NF-5B-2000.

For operations in Vietnam, the USAF had a dozen F-5As modified with armoured plates underneath the fuselage, different systems and the ability to attach a fixed refuelling probe on the left side of the nose, much like on the CF-5A but then on the other side. At first they had the nick name Skoshi Tiger, but later they were called Tiger I.

Knowing that the Canadians had significantly improved the F-5, Northrop started developing its own upgraded F-5, which became the F-5E Tiger II. Externally, the main differences com­pared to the Freedom Fighters are the mid fuselage contour, smaller speed brakes with a cut-off corner, and the shape of the wing leading edge extensions. The fuselage spine curve line is shorter than on the Freedom Fighter; it stops earlier due to the wider fuselage. The larger leading edge extensions (LERX) have a pointed side. On early production versions the bent is about halfway the side, on later built examples, the point is sharper and closer to the front, giving the LERX an almost no-swept front. The Tiger II has similar engines as the CF-5A, so has louvre doors as well. Usually, the F-5Es have no tip tanks, but launch rails for missiles. For the rest, the changes are inside.

Later built F-5Es could be fitted with the slightly flattened nose of the F-20 Tigershark, that reminds of the nose of a shark. Also, some examples have a triangular dorsal fin.

F-5N is the US navy designation for former Swiss F-5Es that have been converted as adversary trainer. They have the flattened nose and larger LERX of the later model F-5E, but are other­wise externally the same. 

In Iran, the locally built F-5E is called the HESA Azarakhsh. It is externally not different, but may have different avionics.

F-5Es built locally in South Korea are designated KF-5E.

Chilean F-5Es received an upgrade that turned them into the so-called Tiger III. Externally, you can recognise them by the long blade antenna under the nose and the smaller sensors at the side of the nose.

In Chili upgraded F-5E Tiger IIs are called Tiger III. They can be distinguished by non-upgraded ones by the long blade antenna under the nose and the forward looking sensor at the side of the nose. (photo: Chris Lofting/WikiMedia) 

Upgraded Brazilian F-5Es are called F-5EM by them. On the outside, the main change is the longer nose radome, that starts closer to the cannons than on the original F-5E. The overall length of the airplane was not changed though! Also, there is a droplet shaped IFF antenna on the side of the nose of the F-5EM. The right cannon was removed, although this doesn't appear immediately from the outside, as there is a tube for a ram air intake in place. Finally, all F-5EMs have a refueling probe on the right side, but not necessarily a triangular dorsal fin.

The Brazilian F-5EM can be recognised by the longer nose radome, within the same fuselage length, and antennas at the side of the nose. (photo: Palácio do Planalto/WikiMedia)

Modified Singaporean F-5Es are called F-5S. They look the same on the outside as the F‑5EM, including triangular dorsal fin, longer radome and refueling probe.

In Thailand, the F-5TH Super Tigris (formerly known as F-5T Tigris) is the local name for the F‑5E upgrade. Externally, it seems the same as the F-5EM and F-5S, in particular the longer radome, except for the refueling probe that is absent.

F-5E Tiger IV was the name Northrop gave to an avionics upgrade package, that also involves changing the radar, for which the forward buckhead was moved aft to create a larger radome, like described above. Just one test aircraft was flown.

To make room for more camera equipment than on the RF-5A, the RF-5E TigerEye was developed. It has a longer nose than the standard F-5E, and the front part it is lower than the rest of the nose and fuselage. Note that some Saudi F-5Es were fitted with an RF-5A style photo nose but these are not RF-5Es!

In Singapore the RF-5E was upgraded like the F-5E, and then called RF-5S. From the outside there seem to be no differences compared to the RF-5E though, possibly except for the right side refueling probe.

The Tigergazer is the name the Republic of China Air Force gave to F-5Es converted to RF-5E.

For the two seater variant of the F-5E Northrop used a different approach. Instead of using the T-38 forward fuselage, the Tiger II fuselage was stretched by adding a section for the second seat. Hence, the nose of the F-5F is longer than that of the F-5B and CF‑5D. The version also keeps its port side cannon. On the right side, there is a tube for a ram air intake instead. Furthermore new are single wing fences on both wings.

This Swiss Air Force F-5F shows its long nose, typical for only this version. Compare it to the nose of the F-5B and you'll see! Also note the wing fence about halfway the wing. (photo: Peter Bakema/WikiMedia)

These F-5F conversions have similar modifications as the F-5EM and F-5S described above. The radome seems to be the same, but the left cannon is removed and faired over, while on the right side a tube for cooling air remains. Moreover, the F-5FM and F-5T have a refueling probe on the right side.

The F-5FM has no cannon on the left side. The nose is completely flush where it used to be on the F-5F. (photo: Rafael Luiz Canossa/WikiMedia)

In an attempt to further improve the F-5 platform, Northrop built a version with a single, but more powerful engine, the same as used in the Hornet. This version was first named F-5G, and later became the F-20 Tigershark. The single engine with a large diameter meant that the rear fuselage had to be redesigned. The vertical stabiliser is now placed on a thick base, that is a fairing for the braking chute comprtment at the back and a ram air intake at the front. Another change were the higher air intakes, making them appear narrower than those of the F-5. Furthermore, the leading edge root extensions (LERX) were enlarged, giving them an almost rectangular shape. Also, the nose was flattened. Both features later became available for the F-5E, in particular the Swiss operated ones. Finally, the size of the horizontal stabiliser increased by about 30%.

In the end only three prototypes were built, mainly because of the politics in the late 1970s and early 1980s. They slightly differed among each other, as the latter two had a large glass surface on the canopy, extending to the rear edge. 

While the Talon is based on the same Northrop N-156, it is significantly different from the two seat F-5 variants. The N-156T, also called YT-38, and production T-38A have no leading edge root extensions, no leading edge flaps and nothing on the wing tips. Moreover, the air intakes are canted when viewed from the side. Also, the speed brakes are smaller, nearly square and separated from each other. Additionally, the landing gears are slimmer for a flatter fuselage underside, with the nose gear having only half a fork against a double one of the F-5s. Finally, there is an extendable landing light under the nose and a curved plate on top of the ex­hausts.

T-38M is the designation of a Turkish upgraded T-38A with a glass cockpit. Hence, on the outside there are no differences. T-38N (also referred to as T-38A(N)), is a modified variant used by the NASA. They are essentially only different on the inside.

This is a dedicated weapon training vesion of the Talon. It has a pylon under the centre of the fuselage, behind the nose gear. More­over, is has a gun sight, although that is difficult to see from the outside. For the rest the AT-38B is the same as the T-38A on the outside.

The final T-38 variant is the C model, which is a significantly upgraded A or B model. Externally it is best recognised by the perpendicular air intakes, with an oval cross section smaller splitter plates against the fuselage. Additionally, the exhausts have ring-shaped openings halfway the jet pipe. Most T-38Cs seem to have a centreline pylon like on the AT-38B.

Manufacturer HESA from Iran has made this reverse engineered version of the F-5F. Externally, it seems to be the same as the F‑5FM and F-5T, because it has no cannon on the port side of the nose.

HESA made its own, newly built version of the F-5F, called the Kowsar. Compared to the original, it has no cannon in the nose. (photo: Tasnim News Agency/WikiMedia)

One special conversion of an F-5E concerns the Shaped Sonic Boom Demonstrator, that Northrop Grumman made to research sonic booms in relation to airplane shapes. Gone is the typical flat bottom of the F-5, the the demonstrator has a curved underside, from nose until behind the wings.

The NASA Shaped Sonic Boom Demonstrator is clearly based on an F-5E, but then with a whole different forward fuselage. (photo: Valder137/WikiMedia)