- Chinese scientists say they're working on a ultra-fast weapon that is both missile and torpedo.
- It will fly at supersonic speeds and use supercavitation to reach high underwater speeds, they say.
Chinese scientists say they are developing a weapon that is both a supersonic missile and an ultra-fast underwater torpedo.
The concept may be better than the weapon itself. The super-torpedo uses dangerous fuel and sounds similar to a Soviet system that was of questionable value. Nonetheless, the Chinese project sounds impressive.
According to the South China Morning Post, which cited an article in a Chinese aerospace engineering journal by researchers working on the weapon, the missile will be just over 16 feet long and able to cruise at 2.5 times the speed of sound at an altitude of roughly 32,800 feet, traveling up to 124 miles before diving to skim at wave-top level for another 12 miles.
When it's within roughly 6 miles of its target, "the missile will go into torpedo mode, travelling underwater at up to 100 meters per second (200 knots) using supercavitation — the formation of a giant air bubble around it which significantly reduces drag," the Post said. "It will also be able to change course at will or crash-dive to a depth of up to 100 meters [328 feet] to evade underwater defense systems without losing momentum."
The idea of mating a rocket and a torpedo isn't exactly new.
The US RUM-139 VL-ASROC anti-submarine weapon, for example, is a rocket that is launched from surface ships and jettisons a Mark 54 torpedo over a target area. The torpedo floats down to the water with the help of a parachute and then homes in on the submarine.
But the Chinese weapon appears to be a missile that turns into a rocket-propelled torpedo once it hits the water. The missile-torpedo would be powered by a boron-fueled ramjet that could function both in the atmosphere and underwater.
Thus it would be far faster than conventional torpedoes like the US Mk-48, which has a reported speed of around 55 knots.
The problem is designing a propulsion system that functions equally well in the atmosphere and underwater. Researchers at China's National University of Defense Technology believe the problem can be solved by adding boron to the fuel, according to the Post.
"The cross-media ramjet uses a fuel-rich solid propellant, which burns with the external air or seawater entering into the ram to generate high-temperature gas and generates thrust through the nozzle," the scientists said in a paper published in the Journal of Solid Rocket Technology.
Boron is an element found in many substances, from food to detergent and even in human bones. (It has been touted as a cure for osteoporosis.) It also generates a great deal of energy when mixed with other substances to create a fuel.
But as might be expected with such an energetic substance, boron is nasty stuff. In the 1950s, the US Air Force and Navy examined boron-based jet fuel — "zip fuel" — for aircraft such as the proposed B-70 supersonic bomber.
The idea was eventually dropped because boron-based fuel was volatile, corrosive to engine parts, and toxic to humans.
However, the advent of hypersonic missiles has created a need for a lightweight but powerful fuel. Some scientists today believe that boron can be tamed to meet that need. In 2021, for example, the US Navy solicited ideas for boron-based fuel.
Interestingly, the Chinese team has actually increased the amount of boron in the missile-torpedo's fuel.
"Boron usually accounts for about 30 percent of the total fuel weight in an air-breathing missile because of the many other chemicals required to control and prolong the strong combustion," the Post notes, but the research team "doubled the share of boron in the fuel and estimates the result could produce a thrust greater than that of aluminum in water."
The other significant aspect of the proposed Chinese weapon is that once underwater and behaving as a torpedo, the weapon will use supercavitation, which uses engine exhaust gases to surround the torpedo with a bubble, reducing drag and allowing it to achieve high underwater speeds.
The most well-known example was the Soviet Shkval ("squall") torpedo: Rather than using propellers or pump-jets for propulsion like conventional torpedoes, the Shkval was an underwater rocket.
Shkyal was developed in the 1960s and is still in service with Russia's navy. It reportedly has a speed of speed of 200 knots.
While Western navies initially worried that their aircraft carriers and submarines couldn't evade such a fast weapon, the Shkval may actually be a bit of a dud: It has a short range and is unguided, which makes it difficult to hit moving targets.
That may be why the US ended its tentative research into supercavitating torpedoes a decade ago, even as Russia continues to develop supercavitating weapons. A missile that doubles as a torpedo may be too good to be true.
Michael Peck is a defense writer whose work has appeared in Forbes, Defense News, Foreign Policy magazine, and other publications. He holds a master's in political science. Follow him on Twitter and LinkedIn.