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Japan expands underwater defense capabilities with eye on PRC

Marc Jacob Prosser

Tokyo is increasingly focused on maritime security and underwater defense capabilities as regional tensions, particularly the People’s Republic of China’s (PRC) naval aggression, loom large.

Japan will develop autonomous underwater vehicles (AUVs), along with advanced submarines and anti-submarine technologies, while boosting collaboration and interoperability with allies and partners, according to Prime Minister Fumio Kishida’s Cabinet Office.

Tokyo’s strategic positioning includes the need to enhance undersea monitoring and ensure the security of its shipping lanes and other sea lines of communication, vital arteries for international trade and economic stability.

Analysts say the initiatives could significantly boost Japan’s underwater capabilities and improve the nation’s joint defense capabilities with its longtime ally the United States.

“Increasing the ability to visualize the surrounding ocean and what happens within it is crucial to responding to potential threats, such as a submarine,” Bonji Ohara, a senior fellow at the Sasakawa Peace Foundation, told FORUM.

Tokyo’s plans call for domestic production of three types of AUV by 2030: an advanced model for deep-sea operations, a smaller model for shallow water and specific-purpose models. The Japan Maritime Self-Defense Force said the vehicles will conduct surveillance, seafloor topography mapping and environmental monitoring, among other tasks.

Japan has undertaken joint research on underwater drones with Australia, The Japan Times newspaper reported. Collaboration goals include interoperability and information sharing. Japan’s undersea defense initiatives also include trilateral cooperation with South Korea and the U.S. on potential submarine threats, with the countries recognizing the challenges posed by Beijing’s maritime activities.

Disputes between the PRC and other littoral states over sea lanes and maritime territories have spiked tensions. In November 2023, Canberra accused a Chinese warship of causing injuries to Royal Australian Navy divers by using its sonar near them as they cleared fishing nets from their ship’s propellers.

The specter of Beijing potentially expanding its ballistic-missile submarine presence in the Sea of Japan presents additional security conundrums for Japan, which has responded with investments in underwater defense assets, including Taigei-class submarines equipped with advanced technologies.

Japan’s addition of an AUV fleet could be a game changer for the region’s maritime power balance, Nozomu Yoshitomi, a professor in Nihon University’s College of Risk Management, told FORUM.

He noted that while Japan has 22 active submarines, deployment cycles mean the number operating at any given time is lower. The vessels patrol vast stretches, including the East China Sea, the Sea of Japan, the Sea of Okhotsk and the Western Pacific.

The low detectability and high endurance of AUVs are a strategic advantage in surveilling critical maritime chokepoints and protecting underwater assets, such as communication cables.

“The AUV fleet could be one of the solutions to this challenge,” said Yoshitomi, a retired major general with the Japan Ground Self-Defense Force. “This would be very helpful for allies such as the United States and a nightmare for China, preventing its submarines freedom of operations.”

Marc Jacob Prosser is a FORUM correspondent reporting from Tokyo.

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