Chinese military researchers have made waves this week by claiming to be on track to build a next generation submarine that can travel at speeds exceeding 3,000 mph (that’s Shanghai to San Francisco in less than two hours). US weapons experts, however, have dismissed the claims as ‘ludicrous’.

The proposed submarine design would work by applying the concept of supercavitation – a method of speedy underwater travel that was first developed by the Soviets in the 60s, but that has only previously been fitted to torpedoes.

The method works by using a special nose cone to expel air at high volume at the front of the vessel, creating a bubble of gas that surrounds the craft. As air is so much thinner than water the vessel can move much faster while in this bubble (think about the difference between moving your hand through water in a swimming pool and swishing it through the air).

There’s a lot of difficulties that accompany this method (the craft has to already be travelling pretty fast to compress the air, and once supercavitation begins its near impossible to steer as rudders need water to work) but it would be a staggering leap forward for submarines – craft that typically don’t go much faster than 46 mph.

But while having a sub equipped with nuclear-missiles that can circumnavigate the world in half day would certainly be a game changer for international politics, the Chinese claims go way beyond current technology.

A normal submarine vs a supercavitating sub. Image credit: South China Morning Post

Compare the top speed of 3,000mph with the Russians’ supercavitating torpedo, the Shkval, which is many time faster than traditional missiles but still only has a top speed of 230mph. Even the speedier, German version (the superbly named Superkavitierender Unterwasserlaufkörper) can only travel at speeds of up to 249 mph.

In addition, Chinese researcher Li Fengchen of the Harbin Institute of Technology's Complex Flow and Heat Transfer Lab claims his team have solved the problem of steering by showering water on the craft to create a ‘liquid membrane’, varying the friction this membrane creates on different parts of the craft to steer it.

“Our method is different from any other approach, such as vector propulsion," or traditional engines, Li told the South China Morning Post. "By combining liquid-membrane technology with supercavitation, we can significantly reduce the launch challenges and make cruising control easier."

All of which is great in theory, but with the specifics of the research a secret (and the technology itself also unseen) it’s no surprise that some have reacted sceptically to the claims.

Norman Friedman, a weapons expert with the US Naval Institute, told Time: “The idea that any Chinese research association would talk about its best ideas is ludicrous beyond words."

Friedman points out even supercavitating torpedos are only good for a sprint and are incapable travelling much further than 10,00 yards. He adds that the extra space on a sub might be able to extend this range to 40 miles or so, but to drastically increase this distance and the speeds moves the Chinese claims from academic research to science fiction.