A size comparative between the Panzer V [Tiger] and the P-1000 [Ratte]
The potruding barrels in the latter are 8x37mm Flak guns
On June 23, 1942, Dir. Dip. Ing. Grote (along with Dr.Hacker) from the Ministry of Armament, who was responsible for the production of U-Boote suggested the development of a tank with a weight of 1,000 tons. Hitler himself expressed interest in this project and allowed Krupp to go ahead with it. The project was designated as the Krupp P.1000 (Ratte - Rat). This behemoth "land cruiser" would be 35 meters long, 14 meters wide and 11 meters high. P.1000 would be equipped with 3.6 meters wide tracks per side made of three 1.2 meters tracks, similar to those used in excavators working in coalmines. It was planned to power P.1000 with two MAN V12Z32/44 24 cylinder Diesel marine engines with total power of 17,000hp (2 x 8,500hp) or with eight Daimler-Benz MB501 20 cylinder Diesel marine engines with total power of 16,000hp (8 x 2,000hp). According to the calculations, this would allow the P.1000 to travel at maximum speed of 40 km/h. P.1000 would be armed with a variety of weapons such as: two 280mm gun (naval gun used on Scharnhorst and Gneisenau warships), single 128mm gun, eight 20mm Flak 38 anti-aircraft guns and two 15mm Mauser MG 151/15 guns.
The Landkreuzer P. 1500 Monster was a pre-prototype ultraheavy tank meant as a mobile platform for the Krupp 800mm Schwerer Gustav artillery piece, in fact, a mobile grand cannon.
If completed it would have easily surpassed the Panzer VIII Maus, and even the extremely large Landkreuzer P. 1000 Ratte in size.
It would have been 42 m (138 ft) long, would have weighed 2500 tonnes, with a 250 mm hull front armor, 4 MAN U-boat (submarine) diesel engines, [though it would only have enough power to reach up to speeds of 10-15 kph] and an operating crew of over 100 men.
The main armament would have been an 800 mm Dora/Schwerer Gustav K (E) railway gun 10 times bigger in diameter than modern tank cannons, and a secondary armament of two 150 mm SFH 18/1 L/30 howitzers and multiple 15 mm MG 151/15 machine guns.
In early 1943, Armaments Minister Albert Speer cancelled both projects. The P.1000 turret alledly ended up at a coastal defence battery Ørland near Trondheim, Norway.
Prior to both the P.1000 and P.1500, in 1939, Krupp began working on other similar projects for a projected series of self-propelled coastal guns for the Kriegsmarine. The series was to include fourteen different platforms designated from R1 to R14. Armament was to range from 150mm to 380mm and they were to be mounted on fully traversable turntables on tracked carriages. One of the designs was the R2 coastal gun armed with a 280mm gun. The series never left the drawing boards for obvious reasons.