A9 was designed by Sir John Carden in 1934, as the successor Vickers Mark II. Trials started in 1936, and production in 1937. 125 tanks were built in total, and saw service from 1938-41. It was the first British tank fitted with a central turret, but it was not particularly successful design or modern, and the tank was very poorly armored (only 14 mm). The weight of the A9 being relatively low allowed it to be powered by a commercially available 9.64 litre AEC bus engine, which gave it a top speed of 40 km/h. It also had a distinctive “slow-motion” suspension system with the triple-wheel bogies on springs mounted with Newton hydraulic shock absorbers. It was armed with a 40 mm (2-pdr) main gun and three machine-guns, one coaxial in the main turret and the other two in separate auxiliary turrets, and it was the first British tank with an hydraulic-powered turret traverse. Combat experience in France in 1940 and North Africa proved that the design had critical drawbacks: it was just too slow, mechanical unreliability and thinly armoured when confronted by contemporary German tanks. Specifications: