and proved difficult to transport. Description The primary requirement for an assault tank is armour, to enable the tank to assault a heavily emplaced enemy. This led to Tortoise having very thick armour, arranged as a one piece casemate to avoid the weak spots of a turret design. This differs from the design of other wartime era assault tanks, the Excelsior tank and Assault Tank T14. Since the Tortoise had a fixed casemate superstructure instead of a turret, it can be classified as a self-propelled gun or an assault gun and not a tank. The crew included a commander, driver, and gunner, with two loaders for the 32-pounder gun and two machine gunners. Internally, it was split into three compartments: the transmission to the front, the crew in the centre and the Rolls-Royce Meteor engine at the rear. The suspension consisted of four bogies on each side of the hull. Each bogie had two pairs of wheels, with each pair linked to a transverse torsion bar. The Merritt-Brown transmission was fitted with an all speed reverse, giving approximately the same speed backwards as forwards. Armament The Ordnance QF 32-pounder gun design was adapted from the British 3.7 inch anti-aircraft gun. The ammunition used a separate charge and shell, the latter a armour piercing shot (APCBC). In tests, the gun was successful against a German Panther tank at nearly . The 32-pdr gun was mounted in a power-assisted limited traverse mounting; rather than being mounted on the more traditional trunnions, it protruded through a large ball mount in the front of the hull, protected by armour. To the left of it was a Besa machine gun in an armoured ball mount. A further two Besa machine guns were mounted in a turret on the top of the hull to the right. Surviving vehicles One of the six prototype Tortoises constructed of mild steel has been preserved at The Tank Museum in Bovington, England. The vehicle is in running condition. A 2011 overhaul saw it running under its own power for the first time since the 1950s. It was shown to the public in June 2011 at Tankfest 2011, the Bovington museum's annual display of running vehicles. A Tortoise, without its gun, lies on the former Kirkcudbright military training area (now a Site of Special Scientific Interest) in Scotland. The location and condition of the vehicle mean that recovery and restoration is