SR U1 class

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.