The Monster was designed for the purpose of carrying the German 800 mm Dora/Schwerer Gustav K. (E) Rail Gun, a massive artillery piece capable of shattering the most well fortified positions. Had this vehicle been completed, it would have been arguably the most deadly German vehicle to have existed. In addition to it's main weapon, the Monster was to be armed with two 150 mm sFH 18/1 L/30 howitzers as a secondary armament, and then multiple 15 mm MG 151/15 and 7.92 mm MG 42 machine guns for defense against infantry and light unarmored vehicles.
To propel the vehicle, four 2,200 MAN M9v 40/46 marine diesel engines were specified. These engine were originally used as submarine engine for the German U-Boats, and would have given the Monster a top speed of 15 km/h. The operational range and storage capacity of the Monster is unknown. A crew of over 100 men would have been required to operate the vehicle, and 250 mm of armor plating was specified for the front of the vehicle's hull, armor thickness in other places are unknown. The length of the Monster was specified to be 42 meters, while the width was to have been 18 meters and the height 7 meters. The total estimated weight of the Monster was 1,500 tons, hence the designation "P.1500".
The Monster was designed in accompaniment to the smaller Landkreuzer P.1000 Ratte, and no variants were ever designed, and an even larger Landkreuzer design is only rumored to have existed.
The Monster was first designed in the December of 1942, following the appearance of the smaller Ratte concept. The design was approved by Adolf Hitler, and work began on it's actual construction in early 1943. However, only months past before Albert Speer, the Minister for Armaments, cancelled the construction of the Ratte and Monster on the account of production costs. By this time, only sections of the tracks of the Monster had been completed, all of which was cut up and used for tracks on the much smaller Panther and Tiger tanks. This was last known German vehicle design of this scale conceived during World War II.