the Swindon No. 3 superheater in 1909. Douglas Earle Marsh carried out a series of comparative tests between members of his I3 class using saturated steam and those fitted with the Schmidt superheater between October 1907 and March 1910, proving the advantages of the latter in terms of performance and efficiency. Other improved superheaters were introduced by John G. Robinson of the Great Central Railway at Gorton locomotive works, by Robert Urie of the London and South Western Railway (LSWR) at Eastleigh railway works, and Richard Maunsell of the Southern Railway (Great Britain), also at Eastleigh. The oldest surviving steam locomotives with a superheater and the first narrow gauge locomotive with a superheater is the Bh.1 owned by the STLB and runs excursions trains on the Mur Valley Railroad in Austria. Urie's "Eastleigh" superheater Robert Urie's design of superheater for the LSWR was the product of experience with his H15 class 4-6-0 locomotives. In anticipation of performance trials, eight examples were fitted with Schmidt and Robinson superheaters, and two others remained saturated. However, the First World War intervened before the trials could take place, although an LSWR Locomotive Committee report from late 1915 noted that the Robinson version gave the best fuel efficiency. It gave an average of coal consumed per mile over an average distance of , compared to and coal for the Schmidt and saturated examples respectively. However, the report stated that both superheater types had serious drawbacks, with the Schmidt system featuring a damper control on the superheater header that caused hot gases to condense into sulphuric acid, which caused pitting and subsequent weakening of the superheater elements. Leakage of gases was also commonplace between the elements and the header, and maintenance was difficult without removal of the horizontally-arranged assembly. The Robinson version suffered from temperature variations caused by saturated and superheated steam chambers being adjacent, causing material stress, and had similar access problems as the Schmidt type. The report's recommendations enabled Urie to design a new type of superheater with separate saturated steam headers above and below the superheater header. These were connected by elements beginning at the saturated header, running through the flue tubes and back to the superheater header, and the whole assembly was vertically arranged for ease of maintenance. The device was highly successful in service, but was heavy and expensive to construct. Advantages and disadvantages The main advantages of using a superheater