The Landkreuzer P 1500 Monster was a purported German pre-prototype super-heavy self-propelled gun designed during World War II.

The P. 1500 was to be 25 m (82 ft) long, weighing 1,800 tonnes, with a 250 mm hull front armour, four Daimler-Benz MB.501 diesel aero engines, and an operating crew of over 100 men.

[citation needed] This "land cruiser” would have been a self-propelled platform for the 800 mm Dora/Schwerer Gustav K (E) gun artillery piece also made by Krupp—the heaviest artillery weapon ever constructed by shell weight and total gun weight, and the largest rifled cannon by calibre.

Development of the Panzer VIII Maus had highlighted significant problems associated with very large vehicles, such as their destruction of roads/rails, their inability to use bridges and the difficulty of strategic transportation by road or rail.

In 1943, Albert Speer, the Minister for Armaments, cancelled both the Ratte and Monster projects due to obvious major problems.