4-4-2+2-4-4
Under the Whyte notation for the classification of steam locomotives by wheel arrangement, a is a Garratt articulated locomotive. The wheel arrangement is effectively two 4-4-2 locomotives operating back to back, with each power unit having four leading wheels on two axles in a leading bogie, four powered and coupled driving wheels on two axles, and two trailing wheels on one axle in a trailing truck. Since the 4-4-2 type is usually known as an Atlantic, the corresponding Garratt type is often referred to as a Double Atlantic.
Overview
The was not a common Garratt wheel arrangement. Only ten were built, all by Beyer, Peacock and Company, the owner of the Garratt patent.| Gauge | Railway | Class | Works no. | Units | Year | Builder |
| Tasmanian Government Railways | M | 5523–5524 | 2 | 1912 | Beyer, Peacock | |
| Entre Rios Railway, Argentina | 6360–6364 | 5 | 1927 | Beyer, Peacock | ||
| Argentine North Eastern | 6645–6647 | 3 | 1930 | Beyer, Peacock |
Usage
Argentina
Eight locomotives were built for Argentina to run on.- Five were built for the Entre Ríos Railway in 1927.
- Another three were built for the Argentine North Eastern Railway in 1930.
Australia
The first Garratt locomotives to be built to the wheel arrangement were a pair of M class passenger locomotives for the gauge Tasmanian Government Railways in Australia in 1912. They were acquired to haul express passenger trains between Launceston and Hobart.The two M class engines were the only eight-cylinder Garratt locomotives in the world. They were difficult to maintain and, despite their haulage abilities and speed, both were withdrawn from service some time after the arrival of the R class Pacific types in 1924. Both locomotives were scrapped and cut up in the late 1940s.