The A30 Challenger was devised during 1942 as a means of mounting the powerful 17 pounder anti-tank gun on the chassis of what was intended to be the British Army's next Cruiser tank, the Cromwell. The subsequent development programme was subject to a degree of controversy as to the role and efficacy of such a vehicle, and, in the event, only 200 machines were ordered. The first examples did not see action until August 1944, and even then they were often viewed only as "stop-gaps" until the arrival of the A34 Comet. However, there were those, especially among its design team at Rolls-Royce in Belper, Derbyshire, who came to believe that the Challenger represented a missed opportunity to provide the Army with an unprecedented combination of firepower and mobility. This book examines the story of what would be an innovative and successful, if somewhat rarefied, tank and its subsequent development as a self-propelled anti-tank gun.