The tank's hull was 10.1 metres (33 ft 2 in) long, 3.67 metres (12 ft 0 in) wide and 3.66 metres (12.0 ft) tall. Weighing about 180 tonnes (180 LT; 200 ST), the Maus's main armament was a 128-millimetre (5.0 in) cannon with a coaxial 75-millimetre (3.0 in) gun and steel armour ranging from 60–240 millimetres (2.4–9.4 in) in thickness. A total of nine were in various stages of completion and two were completed when the war ended, although one version had a planned production run of between 150 and 200. The Maus would have had a crew of five to six.
The principal problem in development of the Maus was finding a powerful enough engine for its weight that could be carried in the tank. Though the design called for a maximum speed of 20 kilometres per hour (12 mph), no engine was found that could power the prototype to more than 13 kilometres per hour (8.1 mph) under ideal conditions. The weight also made it impossible to cross most bridges. It could ford due to its size or submerge and use a snorkel.
The Maus was designed from the start to use the "electric transmission" design which Ferdinand Porsche had used in his unsuccessful attempt to win the production contract for the Tiger I. The initial prototypes used a gasoline engine, the later ones were to use diesel. It drove a massive electrical generator, and together they occupied the entire central rear two-thirds of the Maus' hull, cutting off the forward driver's compartment in the hull from direct access to the turret from within the tank. Each metre-wide track, which used the same basic "contact shoe" and "connector link" design format as the Henschel-built Tiger II used, had its own electric motor mounted in the rear of the hull; the tracks had no direct mechanical connection to the internal combustion engine that powered the Maus.
Due to the uniquely wide tracks used, there was a narrow lengthwise "tunnel" inside the hull under and to the rear of the turret to house the engine and generator of the tank's powertrain.
The amount of armour was substantial, the front lower hull (glacis plate) was about 200 millimetres (7.9 in) thick, sloped at 35 degrees to the vertical. The sides of the hull were 180 millimetres (7.1 in) and the rear 160 millimetres (6.3 in). The turret was 240 millimetres (9.4 in) to the front and 200 millimetres (7.9 in) to the sides, with a roof of 60 millimetres (2.4 in).
The initial plan for the Maus was for the prototype to have been completed by the summer of 1943, with monthly production scheduled to run at five vehicles per month after delivery of the prototype. The work on the Maus would be divided between Krupp, responsible for the chassis, armament and turret and Alkett, who would be responsible for final assembly.
The Maus tank was originally designed to weigh approximately 100 tons and be armed with a 128 mm main gun and a 75 mm co-axial secondary gun. Additional armament options were studied including various versions of 150 mm and 128 mm guns. Hitler himself in January 1943 insisted that the armament be a 128 mm main gun with a coaxial 75 mm gun.
By May 1943, a wooden mockup of the final Maus configuration was ready and presented to Hitler, who approved it for mass production, ordering a first series of 150. At this point, the estimated weight of the Maus was 188 tons. However, there is a story that concerns the main armament of the Maus being changed by Hitler who said that the 128 mm gun looked like a ´toy gun´ when compared to the tank, causing the 128 mm to be replaced by a 150 mm gun.
Development work on the Maus continued, but in October 1943 Hitler cancelled the order, which was followed in November by the order to stop development of the Maus altogether but to continue the construction of the prototypes.
The first, turretless prototype (V1) was assembled by Alkett in December 1943. Tests started the same month, with a mock turret fitted of the same weight as the real turret.
The principal problem with the Maus that emerged from this test was its power-to-weight ratio. There was no engine powerful enough to give it anything like the 20 km/h demanded by the design specifications. The modified gasoline-fuelled Daimler-Benz MB 509 engine used in the prototype was only able to move at 13 km/h and only under ideal conditions. The suspension system used by the Maus also had to be adjusted to enable it to take the tank's weight.
Another issue found was that the Maus was simply too heavy to cross bridges. As a result an alternative system was developed, where the Maus would instead ford the rivers it needed to cross. Due to its size it could ford relatively deep streams, but for deeper ones it was to submerge and drive across the river bottom. The solution required tanks to be paired up. One Maus would supply electrical power to the crossing vehicle via a cable until it reached the other side. The crew would receive air through a large snorkel, which was long enough for the tank to go 45 feet (13 m) underwater.
In March 1944 the second prototype, the V2, was delivered. It differed in many details from the V1 prototype. In mid-1944, the V2 prototype was fitted with a powerplant and the first produced Maus turret. This turret was fitted with a 128 mm KwK 44 L/55 gun, with coaxial 75 mm KwK 44 L/36.5 gun and a 7.92 mm MG34 for anti-aircraft armament. The V1 prototype was supposed to be fitted with the second produced turret, but this never happened.
By July 1944, Krupp was in the process of producing four more Maus hulls, but they were ordered to halt production and scrap these. Krupp stopped all work on it in August 1944. Meanwhile, the V2 prototype started tests in September 1944, fitted with a Daimler-Benz MB 517 diesel engine, new electric steering system and a Skoda Works designed running gear and tracks.
There was also a special railroad car made for transporting the Maus prototypes.
A plan for an anti-aircraft version of the Maus was formed, dubbed the Flakzwilling 8.8 cm Auf Operational use
The working Maus prototypes remained at Kummersdorf and at the proving grounds in Böblingen. In the last weeks of the war the V1 with the dummy turret was captured by the advancing Soviet forces in the vicinity of the western batteries of the Kummersdorf artillery firing grounds. It had been mechanically sabotaged by the Germans before abandoning it.
The Soviet Commander of Armored and Mechanized troops ordered the hull of V1 to be mated with the turret of V2. The Soviets used six 18t German half-tracks to pull the 55 ton turret off the burnt-out hull. The combined V1 hull/V2 turret vehicle was completed in Germany and sent back to the USSR for further testing. It arrived there on May 4, 1946. When further testing was completed the vehicle was taken over by the Kubinka Tank Museum for storage where it is now on display.
It appears that the capture of this prototype had little impact on post-war Soviet tank development. Soviet tank design continued to concentrate on strictly limiting size and weight. The next-generation Soviet tanks had similar levels of protection and armament. The IS-3 heavy tank was armed with a 122 mm gun, but weighed under 50 tonnes. The T-54 main battle tank, which started production in 1947, provided 200 mm of frontal turret armor, 120 mm of frontal hull armor and a 100 mm main gun, while weighing in at less than 40 tons.