In May 1942, Hitler was still insistent about the development of the ultra-heavy tank and decided that the weight limit of 100 tonnes was wrong. A combination of the thickest armour and an extremely powerful main armament were considered to be more important, even if this would cause the weight to be well over 100 tonnes.
In June 1942 Hitler gave his assent to the conceptual design of the tank as a slow-moving vehicle. In the same month, Hitler was shown the first drawings of the Porsche design, with which he agreed in principle. However, he did demand that the armour on the hull floor should be increased to 100mm, and that the main armament should be either a 15cm L/37 or a 10.5cm L/70 cannon. Professor Porsche agreed that the first vehicle would be delivered no later than the 12th May 1943.
In October 1942, the Porsche works submitted plans for two versions of the "Maus" (lit. "mouse"), labelled as vehicle A and vehicle B. The main armament consisted of a 15cm L/37 cannon with a 7.5cm L/24 as secondary armament. The magazine was to hold 42 rounds for the 15cm cannon and 95 rounds for the 7.5cm cannon. The total weight of the vehicle was expected to be 150 tonnes. It was to be equipped with 2 tracks, each 50cm wide and 4.6m long, resulting in a ground pressure of 1.54kp/cm2. The running gear was to consist of 24 double wheels mounted on torsion bars. The drive unit was to consist of a generator and two electric motors. The diameter of the drive wheels was to be 91.8cm. The maximum speed was expected to be 20 km/h, whilst the steepest angle of ascent would be 47%. The Argus Type 5B disc brakes would be installed at the rear in the drive wheels. A Daimler-Benz diesel engine was planned for installation in vehicle A. This had 12 cylinders with a bore of 162mm and a stroke of 180mm, giving a capacity of 44.5 litres. The estimated output would be 1000 bhp at 2400 rpm, which would give a power ratio of 6bhp per tonne. Vehicle B was to be equipped with an air-cooled Porsche diesel engine. With 18 cylinders, a bore of 135mm, and a stroke of 160mm, this had a capacity of 41.5 litres. At 2,000 rpm this should produce 780 bhp, which would give a power to weight ratio of 4.7 bhp/tonne. After further discussions, the »MB 507« engine with an integrated electric generator producing 900 bhp was chosen.
In November 1942 there was a fundamental alteration to Fighting Vehicle Project 205, in that considerably increased power was demanded. In response to this, Daimler-Benz suggested that the DB 603 aircraft engine with a continuous rating of 1375 bhp at 2300 rpm could be used. As the armoured troops were only supplied with 74 Octane fuel, the aircraft engine had to be refitted with new pistons and revised compression ratios. This was designated »MB 509«.
In December 1942, Professor Porsche and Dr. Müller of Krupp made a report on the status of the pre-production preparations for production of the "Mäuschen" (lit. "little mouse") vehicle. The first prototypes were supposed to be ready by the middle of the summer of 1943.
On 4th January 1943 Dr.Porsche was ordered to Hitler in Berlin, where the model of the "Maus" was shown. Hitler was enthusiastic and no changes should be made. So this was the starting shot for production of the "Maus". The target production quantity was set at 10 vehicles per month. Delivery of the line was expected to commence at the end of 1943. A decision was made in February 1943 to mount the 12.8cm cannon as the main armament.
At the end of January 1943 the Army Ordnance Office gave the orders to following manufacturers for the Maus-components: Krupp for hull and turret, Siemens-Schuckert for electrification, Daimler-Benz for the engine, Skoda for chassis, tracks and transmission, as well as Alkett for assembly.
On 2nd February 1943 Dr.Porsche was again ordered to Berlin, where he was told to mount a flamethrower with 1000 litres of flame fuel into the "Maus". Dr.Porsche protested, because this seems impossible to him. But Hitler insisted on that, the flame projector had high priority from then on. The decision for the flamethrower resulted in major changes in the plans of the "Maus", especially a new spring suspension had to be developed together with Skoda, because the flameprojector added 4.9 tons to the overallweight of the "Maus". (After all the flame projector was not installed to the "Maus")
On the 14th May 1943, a wooden model of the armoured fighting vehicle "Maus" was shown to Hitler in Rasteburg. Hitler gave instructions that the turret should be designed in such a manner that any hits below the level of the cannon would not be deflected onto the hull roof. Furthermore, clarification was required as to whether the "Maus" should be equipped with a direct anti-aircraft capability, or whether Flakpanzer (anti-aircraft tanks) should accompany it for protection. The quantity of ammunition carried for the 12.8cm weapon was to be raised from 50 to 80 rounds, and those of the secondary armament (7.5cm cannon) reduced from 200 to 100. In a meeting on the 23rd July 1943, the Waffenamt (government armaments department) said that the »MB 509« would only suffice as an interim solution, and that anything other than a diesel engine would be out of the question long term. In addition to that a performance of 1500 to 1800 bhp would be necessary. In the meantime an order had been placed with Daimler-Benz for 202 »MB 509« engines, delivering 1200 to 1250 bhp. Moreover Daimler-Benz was pursuing another engine project: the »MB 517« diesel engine, of which two examples had been ordered.The construction of the first prototype began at the Alkett works on 1st August 1943, but the first hull from Krupp arrived not before the middle of September 1943 (construction of the second prototype began on the 22nd February 1944).
The first trials began on the 23rd December 1943, for which Armaments Minister Albert Speer had expressly reserved himself the right to give permission for the first test drive. However, the fitters could not contain their curiosity, and so the driver Karl Gensberger drove around the Alkett factory premises without permission. The picture shows the "Maus" returning to the works hall at the end of this test drive. During the test drive, the "Maus" was also turned, the turning circle being 8 metres. Everyone was so impressed that Professor Porsche was telephoned immediately and informed of the successful drive. He however was somewhat annoyed that the "Maus" could not turn on its own axis. At that point, 
engineer Zadnik (pictured in the photo sitting in the driver's position of the "Maus") was fetched from his sick-bed; he was responsible for the electrical drive unit, and after he found and remedied a starter fault, the "Maus" did indeed turn on the spot! Further test drives were carried out in Böblingen until May 1944. While these test drives Hitler ordered that the first complete "Maus" should be ready by June 1944.On 20th March 1944 the second "Maus" arrived at Böblingen and was put aside until the diesel engine for it was delivered. The first "Maus" was completed on 9th June 1944 with the completed turret which was delivered by Krupp on 3.May 1944.
In fact only two examples of the armoured fighting vehicle "Maus" were produced, but preparations had already been made for the production of a series of 150 vehicles.
Great importance was attached to employing the best armoured protection. The glacis plate was 200mm thick, its strength increased via installation at an angle of 55° to an equivalent strength of armour 350mm thick! The nose plate was of the same thickness but installed at an angle of 60°.
The hull consisted of inner and outer side plates, of which the inner plates were 180mm and the outer plates 100mm thick. The hull roof and the hull floor were 100mm thick at the front, but only 50mm thick at the rear. The turret mantlet was 240mm thick, with 200mm side and rear plates, the side plates being inclined at a 30° angle and the rear wall being inclined at 15°. The turret alone weighed 51.7 tonnes.The suspension for this vehicle was developed by Krupp and consisted of 24 suspension units with a total of 48 wheels. The diameter of the wheels was 550mm and the distance between the wheels 530mm. The wheels were steel wheels with rubber ring inserts. The tracks were developed by Alkett, each track measuring 110cm across and weighing 6.25 tonnes. With a track length of 5.88m and a total weight of 187998 kg, the resulting specific ground pressure of 1.31kg/cm2 proved disadvantageous over rough ground (as can be seen from the photo on the right, where a "Maus" has sunk into marshy ground. However, it did manage to extricate itself under its own power later on). In spite of its heavy weight, the "Maus" achieved a maximum speed of 20 kph. The grade climbing ability was 30° and the step climbing ability was 76cm.
The enormous weight also made the use of bridges impossible, which is why the vehicle had to be equipped for wading rivers. In order to minimise development effort, the decision was made to supply electricity to the electric motor of any "Maus" forging a river by using a cable attached to a second "Maus" standing on the riverbank. The "normal" fording depth of the "Maus" was 2 metres.A new development by Krupp was used as the secondary armament, namely the 7.5cm KwK L/36.5, which was installed to the right of the main weapon. In addition, a MG34 was hung in a frame to the left of the gun cradle. Furthermore, a close defence weapon was built into the
roof of the turret, capable of firing Pattern 39 rapid-action smoke grenades, mortar bombs, Pattern 160 orange smoke markers and Pattern R tracer shells. In the rear part of the turret there was stowage for 24 rounds of cartouche ammunition for the 12.8cm weapon. In total the "Maus" was to carry 68 rounds for the 12.8cm weapon and 200 rounds for the 7.5cm weapon.Since the cross-country radius of the vehicle running on internal fuel tanks was only 42km, an ejectable supplementary fuel tank with a 1,000 litre capacity was mounted on the rear wall of the tank hull. This could be jettisoned beyond the immediate combat area by means of a Bowden line.
In October of 1944, the first "Maus" was sent to the Army Evaluation Centre for Tanks and Motorisation at Kummersdorf, while in this time the diesel engine for the second "Maus" arrived at Böblingen, where it was installed and without further testing the second "Maus" also was sent to Kummersdorf. Several drivers, such as Behnisch, Hantschik and Zebitz were given the duty of performing test drives. When the engine of the second Maus was started the first time, it destroyed the crankshaft, which was wrong installed between engine and generator. A new engine arrived in Böblingen not before March 1945, which was instantly installed. As the war approached Kummersdorf in 1945, both examples of the "Maus" were made ready for combat, presumably to get "Maus" no.2 (which had not a complete turret but only a weight-simulation "turret") in safety and got "Maus" no.1 along, which was ready for combat! Both drove off in the direction of Wünsdorf until one of them broke down with drive unit damage at the crossroads of the modern Bundesstraße (Federal Road) 96, direction Töpchin.
A little later this "Maus" was captured intact by the Red Army. This was presumably "Maus" no.2. The other "Maus" travelled a few kilometres further, but was then destroyed by its crew (see picture at left).Because nowadays you can see a complete "Maus" at the military museum in Kubinka (near Moscow), it is thinkable that the russians took the hull of the intact captured "Maus" no.2 and the nearly intact turret (look at the picture) of blown-up "Maus" no.1 and put them together to a complete "Maus".
At the end of the war there were three more examples of the "Maus" under construction, the parts of which were discovered at the Krupp works.
If you're interested in more info or photos, please read the following mentioned books.
