This is the smallest locomotive in the National Railway Museum's permanent exhibition. It played a very specific role, testifying to the importance that the railway had in other sectors. It is a narrow gauge locomotive which operated on 600mm lines and was built in England by the Robert Hudson Company in 1918 as an industrial locomotive. It was built by a partner foundry of the manufacturer and saw military use on the temporary railway lines of World War I, transporting supplies, weapons or ammunition to the front. It was purchased in 1922, by the Carbonífera do Douro Company (E.C.D.). Mining locomotives had names instead of numbers and this one was given the name "Pejão” because it served at Couto Mineiro do Pejão in Castelo de Paiva, where mining was undertaken, and it transported coal from the mine to boats on the River Douro. It was preserved after the end of rail transport.