In the U.S., J. Walter Christie developed a series of fast tanks, based on his revolutionary Christie suspension system. This was combined with very high power-to-weight ratios achieved by fitting large aircraft engines in his tanks. Although his prototypes were capable of very high speeds, and in some cases designed to be air transportable, disputes with the United States Army Ordnance Corps and a high price (compared with what the US military was willing to pay) meant they were never produced in the USA. Christie's prototypes were however purchased by the Soviet Union, and were to be developed into the BT tanks and eventually, on the eve of World War II, the famous T-34. The success of the BT series, when observed by Fuller, at Russian Army manoeuvres, influenced the British to buy a Christie M1931 tank, imported as a "Tractor", which led to Christie's suspension incorporated into British