This OQ class locomotive was built by Peckett & Sons in 1954. Based on tractive effort it is the most powerful steam locomotive design built in Britain. It has been calculated that locomotive has a tractive effort of over 32,000lbs and in British Railways terms would have qualified as a 7F in power classification.
The Stephenson inside valve gear is probably the ultimate design for any locomotives of a classic saddle tank design.
The design was produced to provide heavy shunting locomotives to Port Talbot steelworks but Pecketts did not win the order so 2150 was sold to the National Coal Board (NCB) and utilised at Mardy Colliery where it became Mardy No 1.
Maerdy Colliery was a coal mine located in the South Wales village of Maerdy in the Rhondda Valley. The mining of coal there started around 1875 but closed in 1935. The colliery re-opened in 1938 but closed again in 1940 as it was greatly affected by the suspension of coal exports to Europe during the Second World War.
The mine then lay derelict until after the nationalisation of the coal industry. In 1949 the National Coal Board (NCB) announced a £7m investment in the colliery to access 100million tons of coal. It was transformed into one of the most modern pits in the United Kingdom, with fully electric winding, new extended railway sidings and a coal washing plant on the surface. New underground roads were built which linked the mine to Bwllfa Colliery in the Cynon Valley.
The last coal was raised at Mardy Colliery in 1986 although coal continued to be mined and brought to the surface at Tower Drift Mine, with which it was linked underground. Mardy closed in 1990 and the site has since been demolished and cleared.
The locomotive was withdrawn from industrial service in 1976 and moved to the Swanage Railway.
It was never used at Swanage and in the 1990s the locomotive moved to the to Elsecar Heritage Railway where restoration work commenced.
In 2003 the locomotive was returned to steam at Elsecar. Here the locomotive is referred to as Mardy Monster.
Following a loan period at the Weardale railway it was prematurely withdrawn from service awaiting firebox repairs. The locomotive re-entered service in 2005 and continued to give good service at Elsecar.
In 2010 the locomotive went to the East Lancashire Railway for a brief visit in mid-2010 but proved unsuitable for their 25 mph running, so it became available for hire again and was loaned to the Lincolnshire Wolds Railway the end of October 2010.
At the end of 2014 the locomotive was taken out of service at Elsecar for overhaul. The boiler was sent to Locomotive Maintenance Services at Loughborough for a major overhaul which was completed in 2017 and the boiler returned to Elsecar.
The overhaul of the locomotive is continuing at Elsecar and it is anticipated that it will return to steam in September 2018. The work on the rolling chassis was expected to be completed by April/May 2018 and the reassembly of the locomotive to commence soon afterwards.