China has revealed plans for a new supersonic submarine based on Cold War technology that will travel inside an air bubble to reduce friction.

If successful, researchers believe the submarine will reach up to 3,600 miles per hour. That means that a trip from Shanghai to San Francisco in the submarine will take about two hours.

A scientific team at Harbin Institute of Technology's Complex Flow and Heat Transfer Lab is developing the submarine. However, the submarine's technology isn't new: it's based on Soviet ideas from the Cold War.

During the Cold War, the Soviets discovered a technology that creates an air bubble around a submarine that allows it to "fly" underwater. This air bubble prevents friction, which results in less drag against the vessel, which means it can reach faster speeds. The Russians used this technology, called supercavitation, on some of their torpedoes. Those torpedoes traveled at speeds up to 230 miles per hour.

The Chinese method creates a continuous liquid membrane on the surface of the submarine as it starts moving. That membrane reduces drag until the submarine can reach a speed great enough to create an air bubble around it: this happens around 47 miles per hour. Operators steer the ship by increasing or decreasing the membrane around it by creating different levels of friction against separate parts of the submarine.

However, other details of the submarine are not yet being released.

"These studies in China do not go to academic papers, but the technology is being tested in the laboratory," says Stephen Chen, a reporter for the South China Morning Post. "The scientists have received pressure from authorities due to the sensitivity of the research and they hope the matter can cool down a bit."

Some scientists, though, question if the technology actually works, at least for submarines.

"The size of the bubble is difficult to control, and the vessel is almost impossible to steer," says Wang Guoyu, head of the Fluid Mechanics Laboratory at Beijing Institute of Technology.

The submarine scientists still face several technical issues, however, including creating a rocket engine that will work underwater and have the ability to travel longer distances. Considering that the Russian torpedoes were only able to travel about five miles, this could be their greatest challenge.

Although, the Chinese are using supercavitation for military purposes, the technology could have more commercial applications. Supercavitation could be a viable option for new high-tech swimsuits, for example, making swimming easier and faster. The idea is that the suit would hold tiny air bubbles around the swimmer, reducing drag.