The South Australian Railways 400 class comprised ten 4-8-2+2-8-4 articulated steam locomotives built in France in 1952 and 1953 under licence to Beyer, Peacock & Co. Ltd, Manchester, UK. The locomotives mainly hauled ore on the 1067 mm narrow-gauge line from the New South Wales/South Australia border to smelters at Port Pirie until 1963, when they were replaced by diesel locomotives. They also operated on the line to the break-of-gauge station at Terowie. Some locomotives were returned to service in 1969 while narrow gauge diesel locomotives were converted to 4 ft 8+1⁄2 in standard gauge. Subsequently some were stored at Peterborough before being scrapped.

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, a 4-8-2+2-8-4 is a Garratt articulated locomotive consisting of a pair of 4-8-2 engine units back to back, with the boiler and cab suspended between them. The 4-8-2 wheel arrangement has four leading wheels on two axles, usually in a leading bogie, eight powered and coupled driving wheels on four axles and two trailing wheels on one axle, usually in a trailing truck. Since the 4-8-2 type is generally known as a Mountain, the corresponding Garratt type is usually known as a Double Mountain.