In 1941 a request was made by the Army for a tank that could carry a the 17 pdr / 76 mm gun that was finishing development at the same time. The Centaur / Cromwell chassis was selected for development.
The Cromwell didn't have adequate firepower, so the Challenger was developed to mount the 17 pdr.
Used a Cromwell chassis. Hull was lengthened and another road wheel was added. The width of the hull was also increased. With its extra length it was difficult to steer.
An additional loader was added. To save weight the hull machine gun wasn't included.