Under the Whyte notation for the classification of steam locomotives, 0-2-4 represents the wheel arrangement of no leading wheels, two powered driving wheels on one axle, and four trailing wheels on two axles.

This is a most unusual wheel arrangement, with the only known examples being three locomotives supplied to the 4ft 6in Dundee and Newtyle Railway by J & C Carmichael of Dundee in 1833. These were still in operation in 1847, but may have been scrapped in 1849 when the line was converted to the standard gauge.

Model of the Earl of Airlie

One of the steam locomotives used on the Dundee and Newtyle Railway was Earl of Airlie, a 0-2-4 built by J & C Carmichael of Dundee in 1833. This had a horizontal boiler but the cylinders were vertical and drove the front wheels through bell cranks. It was one of the earliest engines in Britain to be fitted with a bogie. Other locomotives were built by the Dundee Foundry at which James Stirling (1800–1876) was manager.