One of the Mark IIs used as test vehicles had had 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 pumps that in turn powered two (Williams-Janney)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. Steering was easy and gradual however and the version was taken into production to equip one tank battalion. Three were built out of an order for 74 when war ended. The hull was slightly lengthened in comparison with the Mark V. No Mark VIIs survive.