Key Point: Should the U.S. Navy be concerned? Are the days of truly stealth subs over? 

China is making great efforts to detect U.S. submarines.

Scientists at a Chinese research institute say they developed an airborne laser that might eventually detect hostile subs even at great depths.

Meanwhile, scientists at another institute also claim to have developed a magnetic detection device that might spot subs.

Researchers at the Shanghai Institute of Optics and Fine Mechanics say they have tested lasers that can detect objects more than 160 meters (525 feet) beneath the water, or twice as deep as current equipment.

“The Shanghai team used a beam generated by green and blue lasers,” according to the South China Morning Post. “As light – even laser, a pure, coherent form of light – scatters faster in water than in air, the beam must be very powerful to go deep. Laser devices generate an energized beam of light of a single color, or frequency. Green and blue beams can penetrate water with relative ease.

“Chen’s team also developed a highly sensitive detector that can pick up a single photon reflected from a target, allowing the device to detect bright objects close to the surface as well as targets hidden in the deep.”

A team at the Wuhan Institute of Physics and Mathematics say they have devised a magnetic detection sensor that can fit into a capsule the size of a bean. “The device can pick up signals as weak as 20 femtotesla, or about one-fifth the strength of the magnetic field generated by a human brain,” explained the South China Morning Post.

“Although other devices known as magnetic anomaly detectors are much more sensitive, they are bulkier and can only be mounted on planes or helicopters,” the Post added. “Magnetic anomaly detectors used in anti-submarine warfare must operate at temperatures near absolute zero and require lasers, power supplies and gas chambers to achieve high sensitivity.”

In 2018, Chinese scientists said they were developing a laser-equipped satellite that could detect submarines. The idea is to use laser beams of various colors that can detect disturbances in the water caused by a moving submarine.

The question is what will make these devices successful when previous efforts have fizzled. For example, in 2010, DARPA's Deep Sea Operations program sought to develop blue-light lasers for undersea  communications and hunting subs. The problem is that orbital laser beams can be affected by clouds, murky water and fish, as well as being scattered in the water.

The new blue-green lasers devised by the Shanghai team reportedly have been tested at lower altitudes, from aircraft flying between 1,500 and 3,000 feet. But aircraft-mounted lasers tend to be low-powered, so it remains to be seen whether the new lasers will be successful in locating deep-diving subs.

As for the Wuhan team’s new magnetic detection sensor, a bean-sized device far smaller than the magnetic anomaly detection (MAD) sensors flown by anti-submarine aircraft would seem to face limitations in power and range.  Even some Chinese scientists contacted by the Post were dubious that the magnetic sensor could be useful without further development.

However, such a bite-sized device could be mounted in unmanned aircraft, raising the possibility of swarms of drones hunting subs. Of course, the U.S. is working on its own sub-hunting solutions, including a yacht-sized robot ship that tracks enemy vessels.

Michael Peck is a contributing writer for the National Interest. He can be found on Twitter and Facebook. This first appeared last year.

Image: Reuters.