Following experience gained in Vietnam it appeared that the US Army needed a dedicated anti-tank helicopter to replace the AH-1 Cobra, that was just an interim solution. The competition was won by the Hughes design, that was designated AH-64 Apache. Hughes model 77 has a slender fuselage, with a sort of cheeks along the lower sides of the fuselage, containing among others avionics. The crew sits under a two part, continuous canopy. The canopy opens at the sides; the top panels are fixed. The pilot in the back sits higher than the weapons operator in the front. Near the middle of the fuselage are two external nacelles with the turboshaft engines. They have a round plug in the intake. Just below are the short stub wings wing two weapon pylons on each. The Apache has a four blade main rotor and a four blade tail rotor as well. This tail rotor has a scissor shape, meaning that the angles between the blades is not equal. Except for the first prototype the tail rotor is placed high on the vertical fin, on the left side, but not at the very top. Below is an all movable horizontal stabiliser. Finally, the AH-64 has a fixed single wheel gear, with a rear braced main gear. The tail wheel it at the very end, below the stabilator.

To distinguish the different versions of the AH-64 Apache you will have to look at

• whether it has high or low mounted horizontal stabilisers
• whether the main rotor blades can be folded or not
• the presence of a dome on top of the rotor mast
• the size of the sponsons or "cheeks" along the side of the fuselage
• the shape of the main rotor tips

The YAH-64 was the helicopter that Hughes made for the tests against the Bell YAH-63. While many feature of the eventual AH-64A are already visible, the YAH-64 is still quite different. For a start, it has a T-tail and a tail rotor halfway the tall vertical fin. Furthermore, the canopy windows are different, as is the nose. Other differences are less obvious. On an updated version of the YAH-64 the horizontal stabilisers are located at the bottom of the tail boom.

The YAH-64 prototype already looks quite like the later AH-64A, but is still more different than the A model is from the D and E model. Especially note the T-tail. (photo: BG Charles E. Canedy, Deputy Director of Operations & Army Aviation Officer, Office of the Deputy Chief of Staff for Operations & Plans, Washington, DC/WikiMedia)

The key feature of the original Apache, the AH-64A, are the size of the sonsons, or "cheeks" along the lower sides of the fuselage. They start near the front of the canopy , become higher and wider from there and end again below the stub wings. The main rotor tips are swept, but the chord remains the same as the main part of the rotor blade, i.e. both leading edge and trailing are swept with the same angle.

On this upgraded Apache, the sponsons are much longer, starting at the sensors in the nose and continuing until after the stub wings. On the left side they are higher than on the right side. Moreover, The AH-64D can be equipped with the Longbow radar (hence the name), housed in a dome on top of the main rotor mast. Not all AH-64Ds are actually always fitted with this dome, so the size of the sponsons are the main recognition point, together with the main rotor tips. These are the same as on the AH-64A.

The UK version of the AH-64D was largely license-built by Westland, and called WAH-64 by them. In military service it became the Apache AH1 though. This version has different engines, but in externally the same nacelles. Additionally, it may have some different sensors, but as these have changed in the course of time (also on other AH-64Ds!), it is difficult to tell how you can use them to recognise an Apache AH1. Anyway, the British Apaches seem to always have the Longbow radar installed.

The third generation Apache is externally quite similar to the AH-64D, but has different main rotor blades. They are thicker and only the leading edges of the tips are swept, meaning that the tips taper. The UK equivalent of the AH-64E is the Apache AH2. So far, we still need to find out the external difference between the AH-64E and Apache AH2.