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Soviet engineering is often considered simplistic but effective - yet this beast of a boat-plane hybrid was anything but.

The KM, dubbed the Caspian Sea Monster by US Intelligence services, was a one-of-a-kind monstrosity, measuring 240 feet long with a 144 foot wingspan.

Capable of carrying 137 tons of troops and equipment, including as many as six nuclear missiles, the beast had a weapons pay load of a ship and the speed of a plane, according to What On Earth.

It could travel at speeds of up to 350mph, albeit only 16 feet off the surface of the water - which in turn made it a deadly weapon.

The craft flew so low it travelled underneath traditional radars and so was impossible to see it coming until it had arrived.

(Image: SCIENCE CHANNEL / WHAT ON EARTH?) (Image: SCIENCE CHANNEL / WHAT ON EARTH?)

While much more is known about the KM now, the giant super weapons baffled CIA and intelligence service when first released by the Russians.

US military bosses first detected the weapon through satellite images over the Caspian Sea - hence its loving nickname.

The CIA were supposedly so concerned about the discovery, the agency set up its very own task force to uncover the secrets behind the new weapon.

And they even developed their own surveillance technology specifically for the operation, including the KM drone known as the Aqualine.

(Image: SCIENCE CHANNEL / WHAT ON EARTH?) (Image: SCIENCE CHANNEL / WHAT ON EARTH?) (Image: SCIENCE CHANNEL / WHAT ON EARTH?)

First photos taken by American satellites showed the strange aircraft carrying the letters kM - which was thought to mean ‘Kaspian Monster’ but actually meant ‘Korabl maket’ - which translates as prototype ship in Russian.

And although the US only uncovered the beasts secrets in the 1980s, KM testing first began in 1966 - with the first flight performed by the man who designed it, Rostislav Alexeyev.

Despite its impressive statistics, and the fact it looked as if it were built to fight Godzilla not the US Navy, the Caspian Sea Monster was never put into production.

And in 1980, the ship-come-plane crashed and sank in an accident blamed on pilot error after 14 years of service.