Cruiser Mk VIII Challenger The Tank , Cruiser , Challenger ( A30 ) was a British tank of World War II . It mounted the 17 Pounder gun on a chassis derived from the Cromwell tank to add heavier anti - tank firepower to the cruiser tank units . The design compromises made in fitting the large gun onto the Cromwell chassis resulted in a tank with a powerful weapon , but with less armour . The extemporised Sherman Firefly conversion of the US - supplied Sherman to take the 17 pounder was easier to produce and , combined with delays in production , meant that only 200 Challengers were built . However , it was able to keep up with the fast Cromwell tank and was used alongside them . History . The driving force in the development of Challenger was Roy Robotham . Robotham had been a Rolls - Royce executive in the car division who , with no work to do , had led a team to develop a tank powerplant from the Rolls - Royce Merlin aircraft engine . The Rolls - Royce Meteor gave the British a powerful reliable engine , which would power the A27M Cruiser Mk VIII Cromwell tank . Robotham ' s contributions gained him a place in the Ministry of Supply and on the Tank Board , despite his lack of experience in tank design . Initially , Vickers had been working on a " High Velocity " gun to be fitted to the Cromwell , but it was realised that the Cromwell ' s turret ring was too small to mount it . There were longer term plans to develop improved tanks to replace the Cromwell - this would deliver the interim Comet tank and , at the end of the war , the Centurion tank . The General Staff brought forward specification A29 for a 17 pounder armed cruiser tank . This was passed over for the alternate specification , A30 for a 17 pounder armed tank . In 1942 , an order for a 17 pounder gun armed tank was placed with Birmingham Carriage & Waggon expecting it to be based on the A27M components . Turret and gun mounting was in the hands of Stothert & Pitt . Birmingham Carriage had to modify the Cromwell hull to take a bigger turret . Design . The hull machine gun was removed to provide stowage space for the long 17pdr cartridges . It was expected this larger ammunition , together with its stowage forward , would require two loaders and hence a larger turret . To accommodate the large weapon and a second loader , a turret larger than that of the Cromwell was required and the hull had to be lengthened ; and an extra road wheel added . This change in length , without a corresponding change in width across the tracks , reduced mobility compared to the Cromwell . In order to keep the weight under control , compromises had to be made and armour ing was reduced . It was not possible to reduce hull armour , so it was reduced on the turret - 63 mm on the front and 40 mm on the side compared to 75 mm and 60 mm on the Cromwell . As the base of the turret was unprotected , a jacking feature was fitted to clear any jam resulting from enemy action . The first Challenger was completed in 1942 . When the second was tested at Lulworth , it was criticized that , although it would be effective at long range against the current best - gunned tank in German service ( the Panzer IV " Special " with the long 75 mm gun ) , at shorter ranges it would be at a disadvantage due to slow firing rate and thin armour . An order for 200 was placed in February 1943 . In November of that year it was announced that no more would be ordered . Service . Unfortunately , due to some short sightedness , no provision had been made for deep wading trunking and the A30 was unable to participate in the Normandy landings ; the tank had to wait until ports had been secured and the Mulberry harbour s completed . The Challenger , despite its high centre of gravity , was liked by its crews as it was somewhat faster and more agile than the equivalently armed Sherman Firefly . The Firefly design , which had been a backup , proved to be easier to build and production of the Challenger was stopped with about 200 built . Many of the A30s were issued to units using Cromwells , which eased maintenance as they shared many parts . As well as with British units , the 1st Czechoslovak Armoured Brigade which was supplied by the British , used the Challenger in its operations besieging Dunkirk . After the war ended , the Czechoslovak government purchased 22 Challengers from the brigade wartime inventory , and these vehicles continued to serve in the postwar Czechoslovak army ( first with 11th , later with 23rd Tank Brigade and finally they were concentrated into the 13th Independent Tank Battalion ) until retired to the reserve in 1951 and finally scrapped in 1959 . The 1st Polish Armoured Division received a few in mid - 1945 . Variants . The Avenger or SP 17pdr , A30 ( Avenger ) was a variant on the Challenger idea with a differently shaped open topped turret to help reduce weight . With priority production at Vauxhall Motors for the Comet tank , those built in 1945 were not ready for use until after the end of the war in Europe . Some 250 were built and these formed part of the BAOR in Germany . Survivors . Two vehicles survive . One is at the Overloon War Museum in the Netherlands . The other is awaiting restoration at the Isle of Wight Military Museum in the United Kingdom . Once restored , it will be displayed at the Bovington Tank Museum .