Manufactured in England by International Model Aircraft (IMA) of Merton in Surrey, and introduced in early 1948 (probably in response to E.D.'s December 1947 introduction of their 2 cc (0.12 cuin.) Comp Special model), the FROG 180 diesel of 1.77 cc (.108 cuin.) displacement was basically nothing more than a bored-out 1 cc FROG 100 diesel. It shared the same design features along with an identical stroke - in fact, the bottom end components of the two models were interchangeable. The extra displacement was obtained entirely through a bore increase. The fact that the main castings were identical meant that the FROG 100 and 180 were directly interchangeable in the same model, as indeed was the companion FROG 160 glow-plug variant. Moreover, the extra displacement and performance of the 180 came at a relatively minimal cost in terms of engine weight.
The engine passed through three different variants, the most common of which was the Mk. III version, which featured improved hold-down arrangements for the slip-on cooling jacket. The test of this model which appears elsewhere on this website demonstrates that it was a far more powerful engine than either the FROG 100 or the FROG 160 glow-plug version which were its companions in the range. Performance details may be found in the FROG 180 test conducted collaboratively by Maris Dislers and myself, while full details of the engine's development may be found in my separate article on the early FROG models.