Japan reveals plans for underwater-launched hypersonic missile

An illustration of Japan's future underwater-launched hypersonic guided missile. (Japan MoD/Janes)

Japan has disclosed for the first time plans to develop an underwater-launched hypersonic guided missile.

The move could eventually provide the Japan Maritime Self-Defense Force (JMSDF) with a survivable sea-based hypersonic strike capability.

Plans to develop the weapon were revealed in the Japan Ministry of Defense's (MoD) FY2027 budget request overview document, released on 31 August.

In a section covering stand-off defence capabilities, the MoD included a new project line titled ‘Development of a sea-launched hypersonic guided missile'.

The accompanying description states that Japan intends to develop a derivative of its Type 25 Hyper Velocity Gliding Projectile (25HGP) that can be launched from an underwater platform.

However, no budget figure was disclosed, and the programme remains listed under a special funding request category.

The programme is linked to Japan's broader hypersonic guided missile (HGM) effort, which is intended to provide the Japan Self-Defense Forces (JSDF) with a long-range stand-off weapon capable of travelling at speeds exceeding Mach 5.

In the same budget document, the MoD allocated JPY14.2 billion (USD89 million) for continued HGM development activities and JPY167.3 billion for the acquisition of hypersonic missiles and associated ground equipment.

The ministry said the weapon is intended to possess long-range strike capabilities and flight characteristics that make interception difficult.

Notably, the Japan MoD did not specify the intended launch platform for the underwater hypersonic weapon in the overview document.

Instead, it used the broader term ‘underwater platform' rather than explicitly referring to submarines.

This wording leaves open the possibility that the future missile could be deployed from conventional submarines, large unmanned underwater vehicles, or a combination of both.