In the late 1960s, a CIA analyst sat staring at a grainy satellite photograph of the Caspian Sea and could not make the numbers work. The machine in the frame was nearly 100 metres long — longer than a Boeing 747 — yet it was clearly skimming the water, throwing spray, sitting just a few metres above the surface. It had stubby wings and ten engines clustered at its nose. It was not quite a ship and not quite a plane, and nothing in the West's reference library matched it. Someone scrawled a label on the file that stuck for half a century: the Caspian Sea Monster.

The truth was stranger than the espionage. This was no propaganda mock-up. It was a real, flying, 544-tonne machine, and the man behind it had just rewritten the rulebook on how heavy things move over water.

Alexeyev's impossible idea

The designer was Rostislav Alexeyev, a hydrofoil genius from the Central Hydrofoil Design Bureau in Gorky (today's Nizhny Novgorod). His insight was to exploit "ground effect" — the cushion of high-pressure air trapped between a wing and the surface below it. Fly low enough, within a wingspan or so of the water, and drag collapses while lift soars. A craft that could harness it would carry enormous loads at aircraft speeds while sipping fuel.

The result was the KM, short for Korabl-Maket, roughly "ship-prototype." It first ran in 1966 and was, on completion, the largest and heaviest aircraft in the world — a title it held until the Antonov An-225 flew in 1988. Ten turbojets hauled it off the water; eight shut down once airborne, leaving two on the tail to cruise at up to 500 km/h, just metres above the Caspian. Because it never climbed into the radar horizon, it was effectively invisible to the air-defence systems of the day.

Mustard’s superb explainer on the giant ekranoplans.

A ship that flew, flown by the man who built it

The Soviet bureaucracy could not decide what the KM was. Technically an aircraft, it was handed to the Navy, documented as a marine vessel, and christened with a bottle of champagne smashed across its nose like a destroyer. Its first flight, on 16 October 1966, was made partly by Alexeyev himself — almost unheard of for a Soviet chief designer, most of whom never went near the controls of their creations.

For Alexeyev, ground effect was not a gimmick but a third way of travelling, sitting between sea and sky.

The KM was tested relentlessly on the Caspian for some fifteen years. Then, in 1980, pilot error during a manoeuvre sent the giant slamming into the sea. Remarkably, no one was killed — but the machine was wrecked. Deemed too heavy to recover, it was left to float for about a week before sinking. It remains on the seabed to this day, and no second KM was ever built.

The Lun: a sea monster with teeth

The KM had proven the concept, and from it grew something purpose-built for war: the Lun-class ekranoplan, Project 903. Where the KM was a flying laboratory, the Lun was a weapon. Its name means "harrier" — the bird of prey — and it lived up to it. Across its broad back sat six launch tubes for the formidable P-270 Moskit anti-ship missile, a sea-skimming, supersonic ship-killer. The idea was chilling in its simplicity: a machine that could appear from below the radar at 500 km/h and salvo six missiles into a carrier group before anyone knew it was there.

Only one Lun, the MD-160, was ever completed. It entered service with the Soviet Navy's Caspian Flotilla in 1987 and served until the late 1990s. A second airframe was started but, after the Soviet collapse cut military funding, was reworked into a never-finished rescue craft called the Spasatel. The Lun's fatal flaw was the same one that limited every ekranoplan: it could only fly in calm seas, and it could not climb out of trouble. Beautiful in theory, it was a prisoner of the weather.

The monster crawls ashore

For two decades the MD-160 sat decaying at the Kaspiysk naval base. Then, on 31 July 2020, tugs and pontoons dragged the giant out to sea on a roughly 100-km journey toward Derbent, Dagestan, where it was to become the centrepiece of a planned Patriot Park. The move went badly: the Lun grounded short of its destination and sat beached in the surf for months before finally being hauled fully ashore.

The story did not end in the surf. Russian sources reported in December 2024 that MD-160 would be restored, and by autumn 2025 exterior and partial interior work was reported under way — the last Cold War sea monster being readied as a museum exhibit on the very water it once terrorised.

Period footage of the Caspian Sea Monster skimming the surface in ground effect.

The ekranoplan never conquered the seas the way Alexeyev dreamed. It was too fragile, too specialised, too far ahead of the systems that might have tamed it. But stand beneath the MD-160's missile-studded spine and the ambition is undeniable. The Caspian Sea Monster was the answer to a question almost nobody else had the nerve to ask — and for that, it earns its place among the strangest, boldest machines aviation has ever produced.

Sources: Wikipedia (Caspian Sea Monster; Lun-class ekranoplan); CNN Travel; The War Zone; The Aviationist; Forbes.