the Technical Liaison Officer between Stern, Elles and Anley, contributed to the development of the tank, designing a longer Mark I with Williams-Janney hydraulic transmission; one of the Mark IIs used as test vehicles had used a hydraulic transmission. In October 1917 Brown Brothers in Edinburgh were granted a contract to develop this line of research further. In July 1918, the prototype was ready. Its drive system was very complex. The Ricardo engine drove into Variable Speed Gear Ltd. pumps that in turn powered two hydraulic motors, moving one track each by means of several chains. To ward off the obvious danger of overheating, there were many fans, louvres and radiators. However, steering was easy and gradual and the version was taken into production to equip one tank battalion. Three had been built, and only one delivered out of an order for 74 when war ended. It was passed over in favour of the Mark VIII, which was ordered at the same time. The hull was slightly lengthened compared to the Mark V. No Mark VIIs survive. Mark VIII When Stern was removed from his post following disagreements with the War Office, he was side-lined by appointment to a new department to work on a cooperative design between the Allies – assembly in France, hulls, guns and their ammunition from the UK and other components (principally the engines) from the USA. American involvement in the development of the tank design led to the Mark VIII, also known as "Liberty" or Anglo-American tank (though initially the French were partially involved). The engine, a Ricardo petrol for British tanks and a Liberty V12 for US ones to drive its 37 tons (37.6 tonnes) was compartmentalised from the crew of 12 (later reduced to 10), and the cupola structure included forward and rear firing machine guns. Of a planned (shared production) of 1,500 each, a single British prototype was finished by the end of the war. The British built just 24, the Americans completed 100 between September 1918 and 1920, at the Rock Island Arsenal, at a cost of $35,000 [£8,750] apiece ($430,000 [£226,000] in 2006). About 40 hulls for the U.S Liberty were produced by the Manchester Tank Syndicate, 11 British Type Mark VIII by the North British Locomotive Company. They were used and upgraded until the 1930s, when they were given to Canada for training; some M1917s were sold to the