In 1900, while employed at Lohner Coach Factory, Ferdinand Porsche developed the "Mixte", a 4WD series-hybrid version of "System Lohner-Porsche" electric carriage that previously appeared in 1900 Paris World Fair. George Fischer sold hybrid buses to England in 1901; Knight Neftal produced a racing hybrid in 1902. In 1905, Henri Pieper of Germany/Belgium introduced a hybrid vehicle with an electric motor/generator, batteries, and a small gasoline engine. It used the electric motor to charge its batteries at cruise speed and used both motors to accelerate or climb a hill. The Pieper factory was taken over by Imperia, after Pieper died. The 1915 "Dual Power", made by the Woods Motor Vehicle electric car maker, had a four-cylinder ICE and an electric motor. Below the electric motor alone drove the vehicle, drawing power from a battery pack, and above this speed the "main" engine cut in to take the car up to its top speed. About 600 were made up to 1918. The Woods hybrid was a commercial failure, proving to be too slow for its price, and too difficult to service. In England, the prototype Lanchester petrol-electric car was made in 1927. It was not a success, but the vehicle is on display in Thinktank, Birmingham Science Museum. The United States Army's 1928 Experimental Motorized Force tested a gasoline-electric bus in a truck convoy.