for all cylinders. As had happened with the N1 class prototype No. A822, No. A890 was modified to this revised specification in 1930 to reduce maintenance costs. Prior to the modification of No. A890, the new locomotives were visibly different by the absence of the outside-to-inside valve linkage assembly and were given larger tenders with a water capacity of , although the slab-front was retained. Further changes were made to the design, as No. A890 featured right-hand drive, impeding forward vision for viewing signals from the footplate. The main batch was produced with left-hand drive to resolve this problem. The main batch could also be distinguished by their higher running plates along the sides of the boiler, compared to the lower version on the rebuild that required larger wheel splashers to cover the tops of the driving wheels. The main batch had also dispensed with the N class/Midland Railway-style double spectacle plates (the small windows on the front face of the cab) that was retained on the prototype, replacing them with one each side of the boiler. The production locomotives also had a flatter top to the dome covers than that seen on the rebuild. The cabside cutaways for driver visibility were also cut into the roof of A890, an arrangement reminiscent of the 2-cylinder U class rebuilds of K class locomotives. The entire U1 class had smokebox snifting valves, a feature previously used on the other Maunsell moguls. The main batch saw the front steps relocated ahead of the cylinders, as opposed to behind on the A890 rebuild, which was another relic of its previous guise as a 2-6-4 tank locomotive. Smoke deflectors were fitted to the whole class from 1933, as with most of the locomotives designed by Maunsell. The smokebox snifting valves were removed by Oliver Bulleid by the end of the Second World War, although the U1 class chimney was used to improve draughting on the other Maunsell moguls. Operational details and preservation The U1 class was a reliable and economical design like its U class predecessor, being similarly capable of speeds in excess of , whilst displaying excellent traction and acceleration characteristics. The trials made by the Southern Railway on the prototype decided the eventual route availability of the class so that they became a regular fixture on the restricted Tonbridge to Hastings route alongside their N1 class cousins. Their route availability also meant that