A rigid base formed by three driving axles ensured a smooth ride on straight tracks without much sideways movement, and а two-axial steering bogie meant good performance on curve tracks.

Operational experience with two-cylinder engines showed that they had a poor starting ability, accelerated comparatively slowly and had a rough ride.

Delacroix decided to use a technical design specification for a locomotive of type 4-6-0 equipped with a four compounding cylinders.

[1] The design included de Glehn compound system,[1] which at that time was used on certain types of express passenger locomotives in Europe.

[1] Not only Ryazan-Ural but Nikolaevskaya, Tashkentskaya (Tashkent), South-Western, and Privislinskaya (Near-Vistula) Railways all placed orders for this type of locomotive in amounts of 8, 20, 8, 5 and 15 respectively.

[1] In 1911 according to the results of the locomotive testing the Putilov factory made a few significant alterations to the design: greater surface area as well as the diameter of the boiler shell, the high-pressure cylinders were enlarged, and a superheater was mounted.

[1] In 1912 the factory built 6 further locomotives with these improved characteristics for Ryazan-Ural Railway, and they were classified as Уу (transliteration: Uu).

[1] The class U locomotives that worked on other railways had the normal 3 or 4 axle rectangular tenders with water tanks and coal box.