The Yorkshire Engine Company Janus is a line of 0-6-0 wheel arrangement, diesel-electric locomotives that weighed 48 long tons and had a maximum speed of 23 mph (37 km/h). The two Rolls-Royce C6SFL diesel engines gave a total power output of 400 hp (300 kW). Each engine had its cooling system at the outer end, and its generator at the inner end. There were two traction motors, each being powered by one generator, thus simplifying the electrical system.

The Rolls-Royce C range was a series of in-line 4, 6 and 8 cylinder diesel engines used in small locomotives, railcars,construction vehicles, and marine and similar applications. They were manufactured by the Rolls-Royce Oil Engine Division headed by William Arthur Robotham to 1963, initially at Derby and later at Shrewsbury, from the 1950s through to 1970s.