The Thorning III sideport diesel of 2.4 cc displacement was one of the most distinctive-looking model diesels of its day. It was manufactured by Thorning Bensen of Helsingør (in English, Elsinore), Denmark, who had previously manufactured the well-known Monsun Standard diesel, also of 2.4 cc displacement. Around 1200 examples of the Thorning III were made during the engine's production life of over three years from late 1946 to mid 1950.

Despite its rather odd appearance (which led to its being dubbed the "U-Boat" by contemporary Danish modellers), the Thorning III started and ran very well, also being both well-made and durable. These qualities led to its becoming the most widely-used model engine in Denmark for several years before being supplanted by later competing models such as the Viking 2.5 cc diesel of 1950. The manufacturer's attempts to develop an improved replacement model were unsuccessful, resulting in the disappearance of the Thorning range at the end of 1951.

Full details of the series of model engines manufactured by Thorning Bensen may be found in a separate article on this website.