The Aki, Japan’s third and newest ocean surveillance ship, is launched at Mitsui E&S Shipbuilding Co.’s shipyard in Tamano, Okayama Prefecture, in January. (Yasuyuki Sasaki)

KURE, Hiroshima Prefecture--Heightened threats from roaming Chinese submarines in the Pacific have sparked a revival of Japan’s long-dormant ship-surveillance program that costs 22.6 billion yen ($205 million).

The Aki, Japan’s first ocean surveillance ship in nearly 30 years, is expected to be deployed to the Maritime Self-Defense Force’s Kure Base here in spring 2021.

“It will work with Japan’s defense partner, U.S. forces, and complements the U.S. Navy in some areas,” an official close to the MSDF said. “Ocean surveillance ships are another emblem of Japan-U.S. cooperation.”

The Aki will be Japan’s third ocean surveillance ship and the first added to the MSDF since 1992.

The construction of the other two ships, the Hibiki and the Harima, was planned during the Cold War.

But after the Cold War ended, demand for such reconnaissance ships sharply diminished--until China’s rise as a military power.

The Aki, along with the Hibiki and the Harima, is tasked with tracking the movements of China’s dozens of submarines and those of other countries lurking beneath the surface.

The gray 67-meter-long catamaran with a standard displacement of 2,900 tons was built at a shipyard in Tamano, Okayama Prefecture.

Of the 22.6 billion yen in costs to build the Aki, 2.3 billion yen was used to buy the Surveillance Towed Array Sensor System (SURTASS) from the United States through Washington’s Foreign Military Sales program, which manages U.S. sales of defense equipment to foreign governments.

SURTASS is part of an undersea surveillance system that tracks submarine movements.

Although the equipment is essential to the new surveillance ship, it is like a black box for the MSDF because Japan’s naval arm has no access to the heart of the undersea surveillance technology.

The Aki will collect sounds from foreign submarines moving deep in waters around Japan through the SURTASS towed by a cable several kilometers long.

The SURTASS can detect propeller whirs of a submarine hundreds of kilometers away. The sounds collected are digitized, and a body of such data is used to identify the model and country of the submarine.

The Hibiki, Japan’s first ocean surveillance ship, was deployed to the Kure Base in 1991, followed by the Harima in 1992.

Japan envisaged the shipbuilding project in 1987 at the strong urging of the United States.

“After the Cold War, a new project to build more (ocean surveillance) ships was shelved,” a person familiar with the MSDF situation said.

The project came back to life in the Defense Ministry’s National Defense Program Guidelines issued in late 2013. The guidelines are compiled every 10 years or so to carve out Japan’s mid- and long-term defense policy.

The purpose of reviving the old program was to “gather intelligence on the Chinese Navy’s submarines,” said another official close to the MSDF.

In 2013, a spate of incidents provided a rare glimpse into where ocean surveillance ships operated, which is a top secret.

In May that year, as many as 15 cases were reported about long lines of fishing boats being severed in the sea around Okinawa Prefecture, Japan’s southernmost prefecture.

Some of the cases were attributed to the cables towing the SURTASS becoming entangled with fishing lines.

Around that time, ocean surveillance ships from the MSDF and the U.S. Navy tracked down what appeared to be a Chinese submarine cruising in waters off Japan’s Nansei island chain between the main island of Kyushu and Taiwan.

The chase began after the MSDF detected the submarine.

Chinese naval activities grew robust around 2008, with an increasing number of ships cruising to the Pacific through waters off Okinawa Prefecture.

Their passage there became more frequent after autumn 2012, when the Japanese government bought the Senkaku Islands in the southern part of Okinawa Prefecture from private ownership.

The Senkakus, a group of uninhabited islands, are also claimed by China, which calls them the Diaoyu Islands.

Beijing has strengthened its naval capabilities by adding more submarines to its fleet.

Jane’s Yearbook, a British publication of countries’ military strength, put the number of Chinese Navy submarines at 69 in its latest estimate.

“There is no doubt that China has grown into a threat to the MSDF and the U.S. Navy,” said a person close to the MSDF.

A consensus among defense experts is that Japan needs more ocean surveillance ships to fully monitor the activities of Chinese submarines.

The Kure Base is home to about 40 vessels, or 30 percent of the MSDF’s overall total of mainstay vessels, with more ships and units with special assignments than other bases.

They include three transport ships working with units tasked to defend Japan’s outlying islands and amphibious rapid deployment brigades.

The Kaga, the MSDF’s largest destroyer, which held a two-month exercise, similar to a U.S. Navy patrol drill, in the Indian Ocean, the Pacific Ocean and the South China Sea starting in summer 2018, is also stationed at the Kure Base.

The base also has a fleet of 11 submarines, which surpasses the MSDF’s Yokosuka Base in terms of the number of the latest submarine model.