British Railways 10100 was an unusual experimental diesel locomotive known informally as "The Fell Diesel Locomotive" (after Lt. Col. L.F.R. Fell, who was one of the designers). It was the joint production of Davey Paxman & Co, Shell Refining & Marketing Co and Lt-Col L.F.R. Fell, built for them by the London, Midland and Scottish Railway at Derby. Sir Harry Ricardo was also involved. By the time it emerged in 1950, nationalisation had taken place and it carried British Railways livery. The locomotive had six diesel engines, four of them used for traction. The auxiliary engines drove the pressure-chargers for the main engines and the purpose of this arrangement was to enable the main engines to deliver very high torque at low crankshaft speed.