This aircraft spans two generations, one from the early 1970s and the second since the late 2000s. It was originally conceived by the aircraft division of Fiat, soon to become part of Aeritalia. The aircraft was designated G222. The G222 was clearly meant as a medium sized military transport aircraft, having a rear loading ramp. The cockpit has quite some windows, both at the feet of the crew and above their heads; the nose is blunt. The tandem main landing gear retracts in streamline bodies underneath/at the side of the fuselage. There is nearly a wheel diameter space between the wheels.

The different versions of the G222 and C‑27J can be distinguish by looking at:

• the shape of the nacelles
• the number of propeller blades
• the presence of a sensor pod under the nose
• the presence of a sensor pod on top of the tail
• the presence of a rectangular observation window near the rear cargo ramp 

The main characteristic of the standard original G222 is that it has three blade propellers. Their nacelles have a typical rectangular extension at the bottom, most likely used for leeting cooling air in. In Italian military service this version is designated G222TCM, while the US Air Force called it C-27A.

G222SAA is a specialised version for fire fighting, with the SAA standing for Sistema Aeronautico Antincendio. The equipment can be quickly installed and uninstalled, so it is hard to recognise a G222SAA other than by seeing it in action.

Another special Italian version is the G222RM, used for calibration of radio and radar installations. RM means Radiomisura in Italian. To perform its task, the G222RM it has a sensor pod under the nose of which the front is transparent.

Lybia wanted to order the G222 but could (most likely) not get American approval for that because of the engines. Therefore, Aeritalia developed a version with Rolls-Royce Tyne engines. This G222T has four blade propellers and differently shaped nacelles, with ring-shaped air intakes as key feature. Sometimes, this version is called G222L.

Designated non-descriptively G222VS, for Versione Speciale, the electronic counter measures and electrocnic intelligence version of the G222 has a distinctive disk shaped pod on top of the vertical stabiliser. Under the nose is an additional sensor, more with the shape of a dome. This variant is sometimes also referred to as G222GE.

The version used by the Italian air force for electronic counter measures (ECM), the G222VS, has a small disk shaped pod on top of the vertical stabiliser and another sensor dome under the nose. (photo: Aldo Bidini/WikiMedia)

The second generation G222 is a completely modernised version, developed by Alenia in response to a USAF requirement. It has many features of the C‑130J Hercules, hence the designation C-27J, but still looks as a version of the original G222. The biggest external change is in the engines, that fit in larger nacelles, and have an exhaust in the rear. They power six blade propellers. The C-27J can optionally be equipped with a refuelling probe above to cockpit. Other changes compared to the G222 are much smaller.

MC-27J is the marketing name for the special forces version. It can be fitted with a pallet-based gun firing through the left rear side door. If this is not visible, than the MC-27J is not distinguishable from the C-27J from the outside.

While the USAF only used the C-27Js for a limited time, it found the US Coast Guard to take over a part of them, even though the USCG already operates the HC-144 based on the CN235. The HC-27J as the version is called is externally the same as the standrad C-27J, but has additional observation windows behind the wings, just in front of the rear loading door.