to a 2-6-0 tender locomotive design at Ashford works in early 1928. The retention of the cylinder arrangement and valve gear lowered conversion costs, and meant that the locomotive could readily meet the route availability specification. Because of Holcroft's position as one of Maunsell's assistants, the new locomotive displayed many Swindon influences, making them similar to Churchward's 4300 class. The Swindon ideas had also been used on the N, K, N1, U and K1 class designs, which included the Belpaire firebox and conical boilers, constructed at the North British Locomotive Works in Glasgow. The similarity with GWR locomotive practice ended there, as a Midland Railway influence could be found in the placement of the locomotive fittings, with water top-feed into the boiler located inside a dome, although a modification was made to the cab area, which was a variation of those featured on the N class and the 0-6-0s of Henry Fowler. The aesthetic aspects of the locomotive were contributed by another of Maunsell's assistants, James Clayton, who had moved to the SECR from the Midland Railway. The new locomotives also varied with the increased amount of superheating surface area, and the outside valves were controlled by Walschaerts valve gear. The rebuilding process involved the removal of the side water tanks, the rear coal bunker and the trailing axles. In featuring similar components to the U class, the U1 was similar in profile, although a slab-front was incorporated above the front buffer beam to house the third cylinder and associated valve gear assembly between the frames. Nevertheless, the U1 retained the driving wheels and general cab layout of the U class, and the Maunsell tender previously used on the N class locomotives, with No. A890 entering revenue-earning service in June 1928. Main batch, differences with No. A890 and modifications No. A890 was the only U1 class member in operation as trials were undertaken to ascertain whether the design should be perpetuated instead of the N1 class for use on the more restricted routes of the Southern Railway. The success of the prototype U1 over the N1 design led to a construction order for a further 20 locomotives to be built at Eastleigh in 1931. Despite the possible weight savings with the Holcroft valve gear, the complexity of maintaining the linkage with the inside cylinder meant that the new class members were fitted with three separate sets of Walschaerts valve gear