The Medium Mark B was a British tank of the First World War developed as a successor to the Whippet, but ultimately unsatisfactory and production was cancelled at the end of the war. The engineer Lieutenant Walter G. Wilson and the industrialist Sir William Tritton had cooperated in 1915 to develop the Mark I, the world's first operational tank. However, when Tritton decided to build the Medium Mark A "Whippet", Wilson was left out. The Medium A was designed by Tritton's chief engineer, William Rigby. The Whippet was a successful design and proved effective but suffered from a lack of power, complex steering and unsprung suspension. Wilson, now a Major, decided he could by himself develop a better tank as replacement: the 'Medium Tank Mark B'. He probably started drawing in July 1917. Major Philip Johnson of Central Tank Workshops was impressed when he was shown a wooden mock-up during a visit to Britain late 1917. The prototype was built by Tritton's firm, the Metropolitan Carriage and Wagon Company, and was finished in September 1918. Designer M Bergman