Thomas Hill rebuilt various 4w Sentinel vertical boilered steam locos into diesel locos. They removed the steam equipment and superstructure, added new buffer beams, shunters recesses steps and side skirts. Above the running plates, new superstructures housed either a 6-cylinder Rolls-Royce engine, torque converter and gearbox or the 8-cylinder Rolls. These locos were allocated works numbers with a 'c' suffix ('c' for conversion). 

Thomas Hill rebuilt nearly a dozen Fowler 0-4-0 diesel mechanical locos as 0-4-0DH, retaining the frame, running gear and some of the bodywork, fitting new engine and transmission and engine cover. These locos also were allocated works numbers with a 'c' suffix.

Thomas Hill also built Vanguards, Titans, and Steelmans amongst others.