The SR U1 class were three-cylinder 2-6-0 ('mogul') steam locomotives designed by Richard Maunsell for passenger duties on the Southern Railway. The fifth member of the Maunsell "family" of standardised moguls and 2-6-4 locomotives, the U1 was the final development of the Maunsell mogul, and marked a continuation of the basic principles established by CME George Jackson Churchward for the GWR. Developed from Maunsell's previous SR U class design, the U1 class shared characteristics with Churchward's GWR 4300 Class. The U1 prototype was a rebuild of the unique 3-cylinder SR K1 ("River") class 2-6-4 tank locomotive, becoming operational in June 1928. The design was part of a drive to create a standard fleet of locomotives using parts interchangeable with other Maunsell-designed classes. The three smaller cylinders increased their route availability over the 2-cylinder U class. The K1 rebuild featured a variant of the Gresley conjugated valve gear, previously trialled on the SR N1 class prototype, designed by one of Maunsell's assistants, ex-GWR engineer Harold Holcroft. The class was to supersede the production of N1 class locomotives because of its good performance, which amounted to an order for 20 more U1 locomotives in 1931. Production was halted at 21 locomotives, the class gaining a good reputation amongst crews, and all were transferred to British Railways (BR) ownership following nationalisation in 1948. They continued to give valuable service until the Kentish main line electrification scheme was completed in the early 1960s. The entire U1 class was withdrawn from service by 1963, and none were preserved. Background Work on the new design of locomotive was undertaken in 1928 following the construction of the first of Maunsell's U class locomotives. Maunsell wished to create a more powerful version with greater route availability than its predecessors. The Southern Railway had inherited routes with restricted loading gauge where the large, overhanging cylinders of a 2-cylinder locomotive could foul the walls of bridges and tunnels. The new locomotive was intended to complement the U class by providing another locomotive capable of undertaking passenger duties on the Eastern section of the Southern Railway network between London and Ramsgate. The new locomotive, like the U and N classes before it, was intended to replace obsolete 0-6-0 classes in an attempt to standardise and ease maintenance by sharing parts with other Maunsell designs. Several K class 2-cylinder 2-6-4 locomotives had been successfully rebuilt as U class moguls, leaving the solitary