Other equivalent classifications are:
UIC classification: 2A2 (also known as German classification and Italian classification)
French classification: 212
Turkish classification: 15
Swiss classification: 1/5
This most unusual wheel arrangement was limited to tank locomotives.
The type appears to have first been used on 14 locomotives supplied to the broad gauge Bristol and Exeter Railway in 1853. They were designed by James Pearson, and featured single large flangeless driving wheels and two supporting bogies. The water was carried in both well and back tanks. Three classes were distinguished by the size of driving wheel; the original 9-foot-diameter (2.7 m) wheels were replaced by smaller ones on later designs. The type was also used on an experimental locomotive by William Dean of the Great Western Railway 1881. It did little work and was prone to derailment. It was rebuilt as a 2-2-2 tender locomotive in 1884.
United States usage
C. P. Huntington was one of three identical 4-2-4 locomotives which were the first locomotives purchased by Southern Pacific Railroad in 1863, for use on light commuter services in the Sacramento area. They were soon deemed too light and lacking in adhesion for most short trains: Their single driving wheel axle did not have the full weight of the engine's rear due to the trailing truck. As a result, they were not used frequently, except when absolutely needed. Also the short water tank on the Forney type frame prevented the locomotives from traveling any moderate distance without consuming all of the water. A sister engine, T. D. Judah was built by the Cooke Locomotive Works in 1863 for a railroad that was unable to pay for it and purchased by the Central Pacific Railroad. It was rebuilt as a 4-2-2 in 1872.
- The little blue engine from the 1906 book The Little Engine That Could was a Forney with this wheel arrangement. Later re-drawn versions of this book sometimes replaced this with the more common 4-4-0 arrangement. Both film versions changed the arrangement to something resembling a 4-2-0 Crampton.
- D. L. Bradley, Locomotive of the London and South Western Railway, Part ii., Railway Correspondence and Travel Society, 1967. pp. 86-87.
- "I think I can. I think I can. - Original 1906 cover". 19 July 2010.
- "The Little Engine That Could, Watty Piper, 1954 - yellow cloth cover with black print".