Researchers in China are reporting that they’ve taken a big step towards creating a truly revolutionary submarine. For years, the nation has been dedicated to the expansion of the People’s Liberation Army Navy (PLAN) Submarine Force. That latest announcement in this plan is the intended development of supersonic submarines. And if feasible, it could a sub to travel from Shanghai to San Francisco – a distance of about 9650 km (6,000 miles) – in just 100 minutes.

The research behind this proposed development comes from the Harbin Institute of Technology’s Complex Flow and Heat Transfer Lab, where researchers are applying a concept known as supercavitation. Originally conceived by the Soviets in the ’60s to create high-speed torpedoes, the Harbin researchers are looking to take things to the next level by applying it to a much larger sea-faring vessel.

As is commonly known, objects moving through water have a harder time than those moving through air. While automobiles are only able to travel so fast before succumbing to wind resistance (aka. drag), surface ships and submarines must content with fluid-dynamics, which are much more tricky. Compared to air, water is far more dense and viscous, which means more energy is required to get up to a certain speed.

Even the most modern and advanced nuclear submarine cannot travel much faster than 40 knots (74 kph/46 mph), and the same applies to torpedoes. Higher speeds are possible, but would require so much power to make it impractical. That’s where supercavitation comes into play, a technique devised with the explicit purpose of creating high-speed torpedoes during the Cold War.

This technique gets around the drag of water by creating a bubble of gas for the object to travel through. In the hands of the Soviet’s, the research resulted in the Shkval torpedo, which uses a special nose cone to create the supercavitation envelope that allows it to travel through the water at speeds of up to 200 knots (370 kph/230 mph) – much, much faster than the standard torpedoes fielded by the US.

The only other countries with supercavitational weapons are Iran – which most likely reverse-engineered the Russian Shkval – and Germany, the creators of the Superkavitierender Unterwasserlaufkörper (“supercavitating underwater running body”). The US is researching its own supercavitational torpedo, but there’s very little public information available. Meanwhile, China is not only looking to create supercavitating torpedoes, but an underwater vessel.

Unlike previous designs, which had to be launched at speeds of 95 km (60 mph) to create a supercavitation bubble, the method described by the Harbin researchers uses a “special liquid membrane” to reduce friction at low speeds. This liquid is showered over the object to replenish the membrane as it’s worn off by the passage of water, and once the object gets up to speed, it would theoretically use the same nose-cone technique to achieve supercavitation.

In theory, supercavitation could allow for speeds up to the speed of sound — which underwater is 5343 kph (3,320 mph) – which would allow a sub to go from Shanghai to San Francisco in well under two hours. For any nation with a nuclear arsenal – i.e. China, Russia, France, the UK, the US – the ability to deploy nuclear missile subs speedily around the world is certainly desirable.

But of course, there are some challenges posed by the concept and any ship that is equipped to run on it. For one, it is very difficult to steer a supercavitating vessel and conventional methods (like rudders) don’t work without water contact. Second, developing an underwater engine that’s capable of high velocity over long distances is very difficult. Jet engines do not work underwater and generally, rockets only have enough fuel to burn for a few minutes.

Nuclear power might be a possibility as far as supersonic submarines go, but that’s strictly academic at this point. Li Fengchen, a professor at the Harbin Institute, says their technology isn’t limited to military use. While supersonic submarines and torpedoes are at top of the list, the same technology could also boost civilian transport, or even boost the speed of swimmers. As Li put it:

If a swimsuit can create and hold many tiny bubbles in water, it can significantly reduce the water drag; swimming in water could be as effortless as flying in the sky.

As always with such advanced (and potentially weaponized) technology, it’s hard to say how far away it is from real-world application. Given that this is primarily a military research project within China, one can expect that it will remain shrouded in secrecy until it is ready. And if civilian researchers are making good progress, then it’s a fairly safe bet that the military is even further along.

While the future of transit is already exciting – what with hyperloops, aerospace travel, robotaxis and robot cars – the idea that people could travel under the waves as fast as on they could on the Concorde is pretty cool! At the same time, the idea that subs equipped with nuclear missiles could reach our shores within two hours is pretty scary. But futuristic military technology has never been known to inspire warm and fuzzy feelings, has it?

Sources: extremetech.com, scmp.com