The Cruiser Tank Challenger (A30) was designed in an attempt to mount the 17pdr gun in a cruiser tank. It wasn't an entirely satisfactory design, but it did enter combat in north-western Europe late in 1944 where the 17pdr gun was a welcome improvement in firepower.
There are two different accounts of the origin and early development of the Challenger. The official version is that very early in 1942 the Birmingham Railway Carriage and Wagon Company, then the parent company for the A27M Cromwell, was asked to develop a tank using as many Cromwell components as possible, capable of carrying the new 17pdr tank gun. The alternative version comes from W.A. Robotham, then the chief design at the Department of Tank Design, and previously a key figure in the development of the Meteor tank engine. He claimed that the Challenger hull had been developed by his department and only constructed by the BRCW.
The Challenger wasn't any wider than the Cromwell, but it did have a wider central fuselage. On the Cromwell the fuselage was entirely contained between the tracks, but on the Challenger part of the central fuselage overlapped with the top of the tracks, creating the space for the larger turret ring needed for the 17pdr turret (on the A34 Comet early attempts to avoid increasing the width of the tank failed, and it was eventually 6in wider than the Cromwell or Challenger). The tank was significantly longer than the Cromwell, and was given a sixth road wheel to compensate (and to decrease its ground pressure). This increase in length without a similar increase in width made the tank rather harder to steer.
Stothert & Pitt produced a very large turret, partly because the 17pdr gun needed quite a lot of space and partly because the War Office insisted on a range of movement from 20 degrees above horizontal to 10 degrees below. The turret needed a 70in diameter ring, 10in bigger than on the Cromwell. It was carried on a large steel ball mounted in a cradle on the hull floor, replacing the standard ball race turret ring used on most other tanks. The bulky turret made the tank look very tall, but this was at least partly a visual illusion – at 9ft 1.25in it was nearly a foot taller than the 8ft 2in Cromwell, but the A34 Comet was 8ft 9.5in tall, while the Sherman was actually 8in taller! This turret was originally used on the TOG 2*, one of the more peculiar British tank designs of the Second World War, although it isn't entirely clear if the turret was designed for the TOG and then used on the Challenger, or designed for the Challenger and briefly tested on the TOG.
By May 1942 three prototypes were under construction. The first was inspected by the Tank Board at Farnborough on 13 August 1942, the second at Lulworth on 21 January 1943. These early trials revealed problems with the large turret, which was difficult to traverse when the tank was parked across a slope. The Chief Inspector, Gunnery at Lulworth considered the entire project to be a pointless waste of effort (partly because of legitimate concerns about the lack of turret armour and the generally cumbersome nature of the tank, but partly because of a misjudgement of the future course of German tank design). Although his conclusions were ignored when the Challenger was placed into construction in February 1943 only 200 were ordered. Its role was eventually taken by the Sherman Firefly, which turned out to be a more practical solution to the problem of fitting the big gun in an existing tank.
Both the Challenger and the Firefly were designed to perform the same task – as a 'hole puncher', to knock holes in German tanks. They were always intended to operate alongside larger numbers of tanks equipped with the 75mm gun (the Cromwell and standard Sherman).
The Challenger was given to some Cromwell-equipped tank regiments serving in north-western Europe. They hadn't been given deep wading gear and so couldn't take part in the D-Day landings. They were first issued in August 1944, but then had to be withdrawn to have a flaw with the front idler-wheel fixed. It soon returned to combat, but didn't make a major impact and many of its users saw it as a stop-gap measure. German reports on its performance are inevitably mixed up with those on the far more numerous Firefly, but it is clear that the Germans feared the 17pdr gun, which could take out the Panthers and Tigers at quite reasonable ranges.
Cruiser Tank Challenger (A30)
Hull Length: 26ft 4in
Hull Width: 9ft 6.5in
Height: 8ft 9in
Weight: 32 tons
Engine: 600hp Meteor engine
Max Speed: 32mph
Max Range: 120 miles road radius
Armament: One 17pdr gun, one machine gun