See LNER class J94 for details.
This locomotive was built in 1944, to a Hunslet Engine Company design, by Robert Stephenson & Hawthorn for the Ministry of Defence.
Initially the locomotive was sent to the Ashington Coal Company by the War Department to help handle the demand for coal.
In April 1952 ownership of the locomotive passed to the National Coal Board Opencast Executive.
In 1955 the locomotive moved to Horton Grange (Northumberland) opencast disposal point before being sent to Swalwell Disposal Point in what was then County Durham (now Tyne & Wear). At the time, the opencast disposal point was
by Mechanical Navvies Limited which gave rise to the name the locomotive carries.
The locomotive next moved to Swalwell in September 1967. This opencast site it worked on became the Metro Centre at Gateshead in the 1980s.
The engine was sold by Johnson’s of Chopwell, who operated the Swalewell site, to the East Somerset Railway and was delivered to Cranmore in August 1973.
It was taken into preservation by 1974 to the East Somerset Railway, where shortly after arrival it was liveried in BR black with the BR number 68005 although it never ran in BR service.
The locomotive was under overhauled between 1974 and 1977 and in May 1989 it was sold to C Adams of Dudley and moved to Birmingham for overhaul.
By 1995 the locomotive was based at the Bolton and Embsay Railway, still in BR black and where it was nicknamed ‘The Mog’. Although overhauled in 2004, a burst boiler tube two years later resulted in the locomotive being taken out of service and stored.
In August 2009 the locomotive was purchased by a Pontypool & Blaenavon Railway member and moved to the Flour Mill for repair the following month.
The locomotive arrived at the Pontypool & Blaenavon Railway in April 2010 and it then worked most of the steam hauled trains on the line.
The locomotive is still based on the Pontypool & Blaenavon Railway and is operational.
In July 2020 it was reported that the locomotive was being assessed for overhaul at the Pontypool & Blaenavon Railway.