The prototype of this model was built to power the flax mills of J. Fergus, Prinlaw Mills, in Leslie, Fife, by J. & G. Thomson, Clyde Bank Foundry. Designed by McNaught, it was a single crank compound working with a 50HP water wheel and was the first compound of this type. This very compact design could only be achieved by placing the HP cylinder directly beneath the crank. Nominally 60HP the cylinders were 22 and 33in. bores by 4ft strokes; steam pressure was 35psi.