The earliest applications of the 15 inch gauge actually date back to the 1850’s. At that time several engine manufacturers built scale models about 1/3 or 1/4 of the size of a main line locomotive of that age as demonstration models. Demonstration models as such, however, came into use much earlier - they are believed to have been invented by Timothy Hackworth in the 1820’s. Hackworth built demonstration models to the proportions of standard gauge engines of his time that ran on 3′ gauge track, so he can be called the inventor of No.3 scale model trains. But that is another story.