There’s a new battle brewing under the waves of the Indian Ocean.

Speculation is rife that India and Japan plan to install a sea wall of “hydrophones”—microphones with sensors, placed on the seabed—between southern India and the northern tip of Indonesia. Hydrophones can record and listen to underwater sounds, with the particularly important ability to track submarine movement.

“I know that there were some talks that were held in the past when I was in service until four months ago,” said Abhijit Singh, a former Indian Navy officer who now heads the Maritime Security Initiative at Observer Research Foundation (ORF), a think-tank in New Delhi. “The Japanese have years of experience operating these hydrophones and the plan is, reportedly, to set them up between the Indira Point (India’s southern-most point) up to the tip of Sumatra in Indonesia.”

Considering the geographic location of the plan—a virtual plugging of the Malacca Strait-Indian Ocean route—and the larger strategic rivalry at play in the region, it is clear that the move is aimed at China. India’s defence ministry is yet to respond to a questionnaire from Quartz.

For a while now, the Indian Ocean has been a theatre of complex strategic manoeuvres between global powers—with India as a key player. From China’s String of Pearls to India’s deepening engagement with the Indian Ocean Littoral, there’s been much churn in recent years.

The US has taken an enormous interest in the region and announced a joint strategic vision with India in January last year. The two nations have put pressure on China for its growing claims in the disputed South China Sea, a strategically vital and reportedly oil-rich 3,500,000-square-kilometre body of water.

“Regional prosperity depends on security,” the joint vision statement said. ”We affirm the importance of safeguarding maritime security and ensuring freedom of navigation and overflight throughout the region, especially in the South China Sea.”

Meanwhile, China itself has plans to build its own “Great Wall” under the South China Sea, through which 30% of the world’s trade passes. On the surface, too, China has been increasingly assertive, having built a string of installations that include airstrips and other military facilities.

The country’s navy has also been making its presence felt in the South China Sea and elsewhere. In fact on June 15, reports said that a Chinese navy spy ship tailed two Indian warships during the trilateral naval exercise between India, Japan, and the US in Japanese territorial waters.