A Garratt (also known as Beyer-Garratt) is a steam locomotive which articulates in three parts. Its boiler is mounted on the centre frame, and steam driven cylinders are mounted on separate frames, one on each end of the boiler. Articulation permits larger locomotives to negotiate curves on lighter rails, due to increased number of axles, that might restrict large rigid-framed locomotives. Many Garratt designs aimed at extracting double the power of the larger conventional locomotives operating on the railways, thus reducing the need for multiple locomotives and crews.
In 1930 Sixteen gigantic ‘N’ class 235 ton Garratt engines were procured by the Bengal Nagpur Railway from M/s Beyer Peacock, Manchester, U.K., for moving heavy mineral traffic. These are the only 4-8-0+0-8-4 Garratt’s ever built, 10 were with Walschaert, 3 with Lentz’s rotary cam gear and 3 with Caprotti valves. Later slightly lighter ‘MN’ and ‘P’ versions of 2-8-2+2-8-2 were procured by BNR. One of the ‘N’ class locomotives is preserved at Kharagpur Workshop. These gigantaic locomotives could easily haul 2400 tons of trailing load on 1 in 100 up gradient.