Typically for a fighter designed in the early 1970s the F-15 Eagle has double vertical stabilisers, cropped delta shaped wings, wedge shaped air intakes at the side of the fuselage and bubble canopy. Distinctive compared to similar aircraft are the tops of the vertical stabilisers, with pencil shaped counterweights pointing forward. They can have different sizes, depending on the exact version. Also the vertical stabilisers are not tilted.

The different versions of the F-15 can be distinguished by looking at

• the size of the canopy and number of seats
• the size of the counterweights on top of the vertical stabilisers
• the number and shape of sensors extending from pylons holding the horizontal stabilisers
• the shape and size of the front blade antenna under the nose
• the presence of fuel tanks at the sides of the fuselage
• the number and location of pylons
• the shape of the main gear wheel rims
• the shape of the nose gear
• the shape of the fairing behind the air brake on top of the fuselage
• the shape of the engine exhausts
• the presence of canards

Note that older versions are sometimes upgrades with features from later variants. This makes a definitive recognition of the right version difficult.

It all started, logically, with the A model, a single seat air defence version of the Eagle. The F‑15A has a cannon in the right leading edge extension of the wing. Missiles can be attached to the corner of the side and underside of the fuselage, and on single pylons under the wings, with each three storage points. Furthermore, the F-15A cannot be equipped with so-called conformal fuel tanks (CFT) along the side of the fuselage. The fairing behind the large air brake on top of the fuselage gradually tapers, giving it more or less a V or Y shape. Finally, the original main wheel rims have more holes than those of the F‑15C. However, many have later been fitted with F‑15C wheels. F-15As of the US Air Force have an ECM antenna on top of the left vertical fin that is larger in diameter than the counterweight on the right fin. Those delivered to other countries, like Israel (where they are called Baz), have equally sized counterweights.

The F-15B, briefly known as TF-15A, is esssentially a two seat version of the F-15A. The canopy it a bit larger above the rear seat, but not much longer. The F-15B can be recognised from the F-15D the same way as the F-15A from the F-15C. And like for other versions the USAF examples have a bigger ECM antenna on top of the left vertical fin than those of other countries.

One special version of the F-15B was the Short Takeoff and Landing/Maneuver Technology Demonstrator (STOL/MTD). At first this aircraft had two dimensional thrust vectoring capabilities, with rectangular exhausts much like the F-22. It also had canards at the sides of the air intakes, with significant dihedral. Later, the 2D nozzles were replaced by 3D ones. These look more like regular exhausts, but slightly different.

Thrust vectoring was first researched on a modified F-15B, with rectangular exhausts. Also note the large, canted canards. (photo: NASA/WikiMedia)

Later, the F-15B STOL/MTD got three dimensional thrust vectoring capabilities, on which the nozzle petal plates could be moved differently. Note they are not covered, like on regular F-15Bs. (photo: NASA/WikiMedia)

The F-15C is a much improved version of the Eagle, although on the outside the differences are limited. As a starter, the main gear rims have only eight large holes. Unfortunately, these can be put on A models as well. Next the F-15C can have conformal fuel tanks along the side of the fuselage, but many don't have them. Finally, the shape of the fairing behind the speed brake has a stepped taper. Originally, the F-15Cs had two similar shaped blade antennas under the nose. On later versions the front was is replaced by a longer, swept one. In Israeli service, these versions are also called Baz. They lack the bigger ECM antenna on top of the left vertical fin.

Israeli F-15C Baz aircraft are the only F-15Cs that are regularly fitted with the conformal fuel tanks, like shown on this photo. (photo: Alan Wilson/WikiMedia)

The two seat version of the F-15C has the same differences compared to the F-15B as the F-15C to the F-15A. Like the F-15C, the F-15D often has no conformal fuel tanks. F-15DJ is the Japanese designation for the two seat license-built Eagle. Like all export versions it has two small diameter mass balances on top of the vertical stabilisers. Moreover, the front blade antenna underneath the nose is longer than on the F-15D. See detail photo at F-15J below.

As a replacement of the General Dynamics F-111 McDonnell-Douglas offered a two-seat bomber version of the F-15D, which won from the F-16XL. This F-15E is usually called the Strike Eagle, thanks to its role. The aircraft is nearly always equipped with conformal fuel tanks (CFT) along the sides of the fuselage. At the underside of the CFTs is a row of three pylons in tandem, with another row of three pylons tangentially at the side. Underneath the air intakes there is room for sensor pods. To carry all the heavy loads, the Strike Eagle has a beefed up nose gear with shimmy damper. The main gear is also larger, necessitating bulged main landing gear doors, although this is not clearly visible. Early models had main wheels with eight large holes like on the F-15C/D, but later F-15Es appeared with fourteen smaller holes. The F-15E retains the Pratt & Whitney F100 engines like the A, B, C and D models. They have typical, uncovered struts to move the nozzle petal plates. This is a way to distinguish the F-15E from (most) later models of the Advanced Eagle series. Originally, F-15Es had only a sensor with a flat, squared off 'knob' extending from the horizontal stabiliser pylon on the right. However, upgrades versions have one of the left as well, with a rounded end.

These are all members of the Advanced Eagle family, a further development of the F-15E that was first introduced as the F-15SA for Saudi Arabia. In US service it has the designation F-15EX Eagle II, and the versions for Israel and Qatar are F-15IA and F-15QA respectively. The Advanced Eagles retain the tandem canopy, conformal fuel tanks and pylon configu­ration of the F-15E. Moreover, it has General Electric engines, with differently shaped and covered nozzle petal plates. Also unlike the F-15E are the similar sized antennas on top of the vertical stabilisers, although these are slightly bigger than say on the F-15J. Advanced Eagles have similar shaped sensors extending from the fairings of the horizontal stabilisers. Both have two knobs. The F-15E has a single knob sensor on the right side only, F-15Ks have a single knob on both sides. The Advanced Eagles have a triangular protrusion between the canopy and the air intake, with an additional sensor. Finally, the Advanced Eagle variants can have two pylons under each wing while all previous versions can only have one. This does not mean that they always have two pylons, making distinction with he F-15SG difficult.

The double sensor 'knobs' in between the engine exhausts and horizontal stabilisers, covered petal plates and similar sized antennas on top of the vertical fins are typical for the Advanced Eagle variants, like this F‑15EX. (photo: USAF/WikiMedia)

Israel's version of the F-15E is much more modified than the 'classic' F-15s and hence they received a different designation, F-15I. The popular name is Ra'am. The F-15I differes from the F-15E mainly in three ways: the small diameter counterweights on top of the vertical stabilisers are like on the export F-15A through D, so both with a small diameter. Additio­nally, there are two sensors extending from between the horizontal stabilisers and engines, with a rectangular cross section at the end. Finally, the F-15I has Pratt & Whitney engines, but with covered struts. The plates are slightly different than those of the GE engine. Note that some F-15Is have a dome shaped antennas directly behind the canopy which makes it easy to recognise an F-15 as an I model.

F-15I Ra'am fighters of the Israeli air force are mostly similar to the F-15E, except for some differences in the antennas on top of the vertical fins and between the horizontal fins and engines. This one additionally has a dome behind the canopy. (photo: Tomás del Coro/WikiMedia)

The F-15J is basically the Japanese license-built version of the F-15C. Externally, it is not much different except for the similar sized counterweights on top of the vertical stabilisers, like on all export F-15s, and the longer front blade antenna under the nose. Unfortunately, upgraded USAF F-15Cs have them as well, but these are swept.

The Republic of Korea Air Force has its own version of the Strike Eagle, called F-15K Slam Eagle. They have similar sized, larger antennas on top of the vertical stabilisers like the Advanced Eagle variants. Also they can have General Electric engines with covered petal plates, but some have Pratt & Whitney engines with uncovered ones. Nearly all have single round knob sensors extending from the pylons holding the horizontal fins. However, photos exist of having only one on the right side.

Most RoKAF F-15K Slam Eagles look like this: with a single round sensor knob in between the engines and horizontal stabilisers on both sides. This one has in addition Pratt & Whitney engines, distinguished by the uncovered nozzle plates. (photo: Republic of Korea Air Force/WikiMedia)

Here is an example of an F-15K with General Eelectric engines (note the covered nozzle plates) and a single knob sensor on the right side only. (photo: USAF/WikiMedia)

F-15S is the designation of the F-15E of Saudi Arabia. Initially, it only differed in the radar and having two small diameter counterweights on top of the vertical fins. However, most F-15S were upgraded with General Electric engines, with covered nozzle plates, and sensors with rectangular cross sectioned ends extending from the pylons holding the horizontal stabilisers. These modifications made the F-15Ss easier to recognise.

The F-15E version for Singapore was the most advanced variant before the Advanced Eagle was developed. Initially, it was called F-15T, but in the end it became the F-15SG. Externally, the F-15SG is essentially the same as the Advanced Eagle variants, except that they cannot have two pylons under each wing. However, as the Advanced Eagles often don't have the second pylon installed, a distinction between the two variants is often not possible. Another, very small difference is an antenna on top of the left wing root, unique for the F-15SG.

Even though the F-15SG is not an Advanced Eagle, it is externally the same except for one small antenna on top of the left air intake, marked by the arrow. (photo: US Dept of Defense/WikiMedia)