Which tank is the heaviest fully enclosed armoured fighting vehicle ever built?

Panzerkampfwagen VIII Maus ("Mouse") was a German World War II super-heavy tank completed in late 1944. It is the heaviest fully enclosed armoured fighting vehicle ever built. Five were ordered, but only two hulls and one turret were completed before the testing grounds were captured by advancing Soviet military forces.

These two prototypes underwent trials in late 1944. The complete vehicle was 10.2 metres (33 ft 6 in) long, 3.71 metres (12 ft 2 in) wide and 3.63 metres (11.9 ft) high. Weighing 188 metric tons, the Maus's main armament was the Krupp-designed 128 mm KwK 44 L/55 gun, based on the 12.8 cm Pak 44 anti-tank field artillery piece also used in the casemate-type Jagdtiger tank destroyer, with a coaxial 75 mm KwK 44 L/36.5 gun. The 128 mm gun was powerful enough to destroy all Allied armoured fighting vehicles then in service, some at ranges exceeding 3,500 metres (2.2 mi).

The principal problem in the design of the Maus was developing an engine and drivetrain which was powerful enough to adequately propel the tank, yet small enough to fit inside it — as it was meant to use the same sort of "hybrid drive", using an internal-combustion engine to operate an electric generator to power its tracks with electric motor units, much as its Ferdinand Porsche-designed predecessors, the VK 3001 (P), VK 4501 (P), and Elefant had.