No. 10100 was an experimental 2,000-hp diesel locomotive originally developed for the LMS, but delivered to British Railways in 1951. Production took place in the old LMS workshops at Derby and Paxman produced the main diesel engines. It was also called “Fell Locomotive” after Lt Col L. F. R. Fell, designer of the special transmission. Goals in the development were a low weight and greatest possible power output even at low speeds.

The main means to achieve these goals was the use of four 500 hp Paxman 12RPH “Hi-Dyne” engines and two additional 150 hp AEC engines which only drove the superchargers of the main engines. The throttle setting on the small engines controlled the flow of combustion air into the big engines, enabling them to produce the highest torque at low RPM. This created a falling torque curve, what resulted in a nearly flat power curve.

Each of the four traction engines had its own hydraulic clutch. Two each were combined by differential gearing, and both groups were combined again with differential gearing to a common gearbox. The clutches of individual engines could be opened, resulting in a variable gear ratio. Then power was transferred to the four central axles.

After testing, the main task of this locomotive were express trains between Manchester and London. Only one year after its introduction, it was out of service for a year due to a damaged gearbox. Later the coupling rods between the two celtral axles were removed. All further development of this concept was abandoned since it did not have much advantage over much simpler locomotives. The prototype stayed in service until it was damaged by a fire in October 1958 and was scrapped in 1960.