| 4-4-2+2-4-4 (Double Atlantic) | |
| Uic/Germany/Italy: | 2B1+1B2 |
| French/Spanish: | 221+122 |
| Turkish: | 25+25 |
| Swiss: | 2/5+2/5, 4/10 from the 1920s |
| Russian: | 2-2-1+1-2-2 |
| Date: | 1912 |
| Country: | Australia |
| Locomotive: | TGM M class |
| Railway: | Tasmanian Government Railways |
| Designer: | Beyer, Peacock & Company |
| Builder: | Beyer, Peacock & Company |
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.
The was not a common Garratt wheel arrangement. Only ten were built, all by Beyer, Peacock & 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 & Company | |
| Entre Ríos Railway, Argentina | 6360–6364 | 5 | 1927 | Beyer, Peacock & Company | ||
| Argentine North Eastern Railway | 6645–6647 | 3 | 1930 | Beyer, Peacock & Company | ||
Eight locomotives were built for Argentina to run on .
After nationalization in 1948, all these locomotives were rostered on the General Urquiza Railway.
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.[1]
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 They were difficult to maintain and, despite their haulage abilities and speed, both were withdrawn from service some time after the arrival of the R class in 1924 and scrapped in the late 1940s.[1]