The KM (Korabl Maket) (Russian: Корабль-Макет, literally "Ship-maquette" or "Model-Ship"), known colloquially as the Caspian Sea Monster, was an experimental ground effect vehicle developed in the Soviet Union in the 1960s by the Central Hydrofoil Design Bureau.

The KM was the largest and heaviest aircraft in the world from 1966 to 1988, and its surprise discovery by the United States and the subsequent attempts to determine its purpose became a distinctive event of espionage during the Cold War.

[1][2][3][4] The KM was among the earliest major ekranoplan (English: "screen plane") projects and was notable for its massive size and payload, becoming the largest aircraft in the world when it was completed in 1966.

[2][6] The KM was at first seen as a promising vehicle specialized for use by military and rescue workers but its design caused many difficulties; progress slowed and Alexeyev moved on to other ekranoplan projects.

Data from The Osprey Encyclopedia of Russian Aircraft 1875–1995,[9] Russia's Ekranoplans: The Caspian Sea Monster and other WiG Craft[1]General characteristics Performance