(CNN) — In the late 1960s, decades deep into the Cold War, US intelligence analysts monitoring the Caspian Sea came across satellite images of an oddly shaped, winged machine of huge proportions.
The unfamiliar structure, a kind of hybrid between aircraft and ship, was quickly dubbed the "Caspian Sea Monster."
What they were looking at was an early prototype of the Soviet Union's Korabl Maket ground-effect vehicle, also known as an ekranoplan.
Ekranoplans make use of "ground effect" -- the aerodynamic forces at play when skimming close to the surface of water -- to achieve fast, but stable, low-level flight.
The Korabl Maket was a mighty example of the genre: Until the Soviet-designed Antonov An-225 came on the scene in 1988, it was the largest and heaviest aircraft ever built.
Retired in 1993, the A-90 Orlyonok Eaglet ekranoplan is on display at the Russian Naval Museum.
In theory, the combination of speed and flexibility could allow ekranoplans to compete with seaplanes and ships. But while they make for a truly awesome sight when in flight, they've so far failed to progress any further than technological curiosity.
The reasons for this range from stability control issues in early prototypes to a lack of industrial scale for economic serial production.
In addition, ground-effect vehicles have traditionally suffered from the same limitations faced by seaplanes when it comes to taking off and landing in rough seas.
It's been almost four decades since Korabl Maket last rode the waters. It was used as a military vehicle by the Soviet Navy and sank in a testing accident in the Caspian Sea in 1980.
However, after years of research and trials, a Singaporean start-up is close to beginning production on a next-generation vehicle that aims to revolutionize coastal transport forever.
Has the ekranoplan's time come?
Fischer's AirFish 3 touches down on water in Narragansett Bay, Rhode Island, in January 1997.
John B. Carnett/Bonnier Corp. via Getty Images
But this isn't the first time ground-effect vehicles have been on the verge of taking off.
While the Soviet Union was trying to develop a military ekranoplan in the 1960s, German engineers were working on their own ground-effect vehicle concept, although this was the product of a private initiative.
Alexander Lippisch, an aeronautical engineer, produced several prototypes with an inverted delta wing design, the Collins X-112, the RFB X-113 and the RFB X-114. However, they were never commercialized.
Lippisch's work was continued by his protégé, Hanno Fischer, who went on to create the AirFish 2 and AirFish 3, both precursors to the AirFish 8.
Fischer managed to complete the first working prototype of the AirFish 8 for an Australian company called Flightship, but it was never serially produced.
Subsequently, the prototype, intellectual property rights and assets were acquired by Singapore-based Wigetworks, who spent the next decade perfecting its design.
Now there are two newly built prototypes of the AirFish 8, a vehicle capable of carrying up to eight passengers and two crew, as well as its smaller sibling, the AirFish 3, which can hold just two people.
Although the roots of both models can be traced back to this decades-old project, they've been through major redesigns and technological upgrades over the past few years.
Despite its ambiguous appearance, the Airfish is considered a ship by organizations such as Lloyd's Register and the International Maritime Organization.
The vehicle is powered by a car engine using conventional unleaded 95-octane gasoline that enables it to fly at speeds of up to 110 knots -- although it usually cruises at lower speeds of around 70 to 90 knots.
This provides a smoother, more comfortable ride for passengers and also prevents it from climbing too high and leaving the ground-effect zone.
Although the legal cruise altitude for ground-effect vehicles set by the International Maritime Organization is nine meters, much of the ground-effect efficiency is lost after an altitude of about six meters.
The AirFish is designed to fly below seven meters (22 feet) at all times, in order to take full advantage of the wing in ground effect.
Its typical cruise altitude on flat water is between 0.5 meters and two meters.
In rougher water with up to two-meter-high waves, the cruise altitude would be about three to four meters above the crest of the waves.
While seaplanes struggle with takeoff and landing when there's a strong swell, the Airfish is more than fit for it. It can take off and land in waves of up to a meter high, says J. C. Goh, an executive director of Wigetworks, who is also a veteran of Caltech and NASA's Jet Propulsion Laboratory.
"We are lowering this to 0.5 meters under normal operational conditions, though, as take off and landing when waves are higher than 0.5 meters can be pretty rough on the passengers," he adds.
What happens next?
China's first ground-effect vehicle, Xiangzhou 1, made its first flight in Sanya in December 2017.
VCG/VCG via Getty Images
At present, Wigetworks is looking to bring investors on board before moving onto serial production.
"We are getting interest from places as far as America and the Mediterranean, but I think for now we will focus on the opportunities nearer to us," says Goh, who adds that they are looking at both the civilian and military markets as potential options.
When it comes to commercial applications, the offshore oil and gas industry or transport operators in island regions such as the Maldives or Indonesia are considered viable avenues for the AirFish.
"We can provide a safe, fast and comfortable means of transportation that's much cheaper than a helicopter or even a seaplane," he adds.
With so few ground-effect vehicles in existence, there isn't a pool of pilots that Wigetworks can draw upon when the occasion arises.
However, Goh plans to rectify this by providing dedicated training to would-be pilots, with experienced sea captains the most likely candidates.
"It's much easier to learn how to pilot the AirFish than it is to do so in an airplane, let alone a seaplane, which can be more technically challenging," he adds.
"As you are never far from the surface, there are less dimensions to care about, you don't need to train for things such as spin recovery or landing in cross winds.
"If there is a technical issue, you would just let it rest on the water and guide it on the surface."
From Singapore to Russia to China
An intercontinental ground-effect vehicle (GEV) during tests at the Moscow Complex of the Zhukovsky Central Aerohydrodynamic Institute (TsAGI) in November 2018.
Stanislav Krasilnikov\TASS via Getty Images
He goes on to explain that most of the airframe is made of carbon composites to prevent corrosion from seawater.
The prospect of fly-by-wire technology has also been rejected, and the avionics are the same as those of a standard small plane.
This economical approach is also extended to the infrastructure requirements.
Instead of dedicated docking facilities, the AirFish comes with its own makeshift low-cost solution, a modular landing station made of plastic cubes that can be built at a cost of little more than $1,000.
Wigetworks isn't alone in resurrecting the ekranoplan. China's first ground-effect vehicle, Xiangzhou 1, was developed for commercial use and made its first flight in December 2017.
Meanwhile, it was reported by the Russian News Agency TASS in July 2018 that Russia is also developing a descendent to the Caspian Sea Monster. The Orlan prototype is a military ground-effect vehicle, armed with missiles, which it plans to have ready by 2027.