As the market for commuter aircraft in the United States grew the Short Brothers saw an opportunity for a thirty seat aircraft, as a larger successor to the Beech 99 and Twin Otter nineteen seater. As Shorts took the existing Skyvan as the basis for the design, the Shorts 330 (officially called SD3-30) retained the basic design features. So the SD3-30 has a square cross section fuselage, though more streamlined especially thanks to the long, pointed nose and and fairing on top of the fuselage, over the wings. The fuselage has large rectangular cabin windows. The cockpit windows are similar to those of the Skyvan. Long, slender wings are attached on top of the fuselage, passing above the cabin. They are braced to the streamline pods for the main landing gear at the side of the fuselage. The rear fuselage slopes up quickly. At the underside is a bagage door, in between the two rectangular vertical stabilisers. The all single wheels gear is retractable, with the main gear retracting in pods next to the fuselage. The engines are housed in large rounded nacelles, with intake under the prop spinner and double exhausts at the top. The engines drive five blade propellers.

The different versions of the Shorts 330 can be recognised by looking at:

• the number of cabin windows
• the cabin door being flush with the side of the fuselage or not

The first two variants of the 330 are the main passenger versions, that mainly differ in the engine subtype. Of course it has many cabin windows. Also the cabin door on the left side is flush with the side of the fuselage. A full view photo of a Shorts 330-200 is at the top of this page.  

UTT in this version stands for Utility Tactical Transport. It has a full width cargo door in the upsloped rear fuselage. Additionally, its cabin door opens inward, to allow it to be used for para dropping. Hence the door is recessed, i.e. not flush with the side of the fuselage.

SD3-Sherpa is the offical designation of the full cargo version of the Shorts 330. It was ordered by the United States Air Force that designated the aircraft C-23A. It can be recognised from subsequent subtypes by the absence of cabin windows, except two immediately behind the cockipt.

Unlike the C-23A the C-23B has as many cabin windows as the normal passenger version. However, it also has a full width cargo door at the underside of the rear fuselage, like the UTT version. Still, it lacks the para dropping door of that variant, making it possible to distinguish the C-23B from other Shoorts 330 versions. 

As the Shorts 330 had already been out of production for a while and the USAF required more Sherpas, Shorts proposed a solution involving the modification of second-hand Shorts 360s, that were abundently available. The USAF accepted this offer and got nearly C-23B+ aircraft, as they were designated. The main changes compared to the Shorts 360 was the removal of a small fuselage plug in front of the wings, and the replacement of the single tail unit with rea fuselage by a newly-built Shorts 330 version, so with an H-tail. The Shorts 360 alreayd had a window in the right rear cabin door and this was retained on the C-23B+. There in no such window on the standard C-23B, so here you have the recognition point.

Avionics upgrade programmes for the C-23B and C-23B+ resulted in two new versions of the Sherpa, designated C-23C and C-23D. Both differ in equipment, but we have found no external differences compared to the C-23B/C-23B+.