Under the Whyte notation for the classification of steam locomotives by wheel arrangement, a 4-6-2+2-6-4 is a Garratt or Union Garratt articulated locomotive using a pair of engine units back to back, with the boiler and cab suspended between them. The wheel arrangement of each engine unit has four leading wheels on two axles, usually in a leading bogie, six powered and coupled driving wheels on three axles, and two trailing wheels on one axle, usually in a trailing truck. Since the type is known as a Pacific, the corresponding Garratt type is usually known as a Double Pacific. Overview Garratt The Double Pacific type was fairly common for Garratt locomotives, especially those intended for faster passenger service. The first of the type was the Class GF, built by Hanomag for the South African Railways in 1927. The first to be built by Beyer, Peacock & Company, the owner of the Garratt patent, was the G class for the New Zealand Railways Department in 1928. Beyer, Peacock & Company also built the last Double Pacific in 1943, for the Nigerian Railways. Union Garratt The South African Railways also operated a Double Pacific version of the Union Garratt articulated locomotive. The Union Garratt was a hybrid locomotive, partly Modified Fairlie and partly Garratt. The front end was of a typical Garratt arrangement, with a water tank mounted on the front engine unit’s frame, while the rear end was constructed in the Modified Fairlie fashion, with the coal bunker mounted on a rigid extension of the locomotive’s main frame and with the pivoting rear engine unit positioned beneath the coal bunker. It had an additional large underbelly water tank under the boiler. The main frame therefore carried the smokebox, boiler, firebox, cab, coal bunker, as well as the underbelly water tank. As a result, like the Modified Fairlies, the Union Garratts were prone to metal fatigue and cracking of the frames. In the case of the Union Garratts, this occurred particularly at the rear, brought about by the long frame overhang laden with the coal bunker. Use Algeria Twenty-nine 4-6-2+2-6-4 Garratts, constructed between 1936 and 1941 by Société Franco-Belge in Northern France, operated until the Algerian independence war caused their withdrawal in 1951. This class, designated 231-132BT, was streamlined and featured Cossart motion gear, mechanical stokers and driving wheels, the largest of any Garratt class. On a test in France, one of