The turret mounted the Ordnance QF 17-pounder gun required in the Tank Board specification and the hull machine gun was removed to provide stowage space for the long 17-pounder cartridges.
The War Office expected that this larger ammunition, together with its stowage forward, would require two loaders, which raised the turret crew to four, the commander, gunner, loader 1 and loader 2.
To fit the larger weapon and additional crewman in the turret, a much larger turret than that of the Cromwell was specified, developed separately, which had a significant effect on the design and was not resolved until later development of Avenger.

To carry the weight of the 17-pounder and ammunition, an extra wheel station and suspension arm was needed, lengthening the hull.
This change in length, without a corresponding change in width across the tracks, reduced mobility compared to the Cromwell, although speed remained high at 25 mph.
To limit the weight, the amount of armour was reduced but this could only be achieved on the turret, 63 mm (2.5 in) on the front and 40 mm (1.6 in) on the sides compared to 75 mm (3.0 in) and 60 mm (2.4 in) on the Cromwell.
The turret did not use a conventional turret ring: to increase the aperture diameter with four inches, it rested on a ball mount on the hull floor.
As therefore the base of the turret was unprotected, and it would cantilever when struck by enemy rounds, a jacking feature, with four internal semi-automatic jacks, was fitted to clear jams.
The additional length allowed larger hatches to be fitted in the hull while still clearing the turret, providing easier access than Cromwell.
The turret mounted the Ordnance QF 17-pounder gun required in the Tank Board specification and the hull machine gun was removed to provide stowage space for the long 17-pounder cartridges. The War Office expected that this larger ammunition, together with its stowage forward, would require two loaders, which raised the turret crew to four, the commander, gunner, loader 1 and loader 2. To fit the larger weapon and additional crewman in the turret, a much larger turret than that of the Cromwell was specified, developed separately, which had a significant effect on the design and was not resolved until later development of Avenger.
To carry the weight of the 17-pounder and ammunition, an extra wheel station and suspension arm was needed, lengthening the hull. This change in length, without a corresponding change in width across the tracks, reduced mobility compared to the Cromwell, although speed remained high at 25 mph. To limit the weight, the amount of armour was reduced but this could only be achieved on the turret, 63 mm (2.5 in) on the front and 40 mm (1.6 in) on the sides compared to 75 mm (3.0 in) and 60 mm (2.4 in) on the Cromwell. The turret did not use a conventional turret ring: to increase the aperture diameter with four inches, it rested on a ball mount on the hull floor. As therefore the base of the turret was unprotected, and it would cantilever when struck by enemy rounds, a jacking feature, with four internal semi-automatic jacks, was fitted to clear jams. The additional length allowed larger hatches to be fitted in the hull while still clearing the turret, providing easier access than Cromwell.
Cruiser Mk VIII Challenger