Japan Plans to Equip Submarines with Hypersonic Missiles
Japanese Prime Minister Sanae Takaichi has presented a preliminary fiscal year 2027 defense budget request to the Diet, the Japanese parliament, which includes reference to an intention to equip Japanese forces with an “underwater-launched,” “high-survivability missile” which can be launched “at an early stage and at long range.” The ambiguous language opens up two possibilities: either a vertically-launched hypersonic ballistic missile, or a torpedo-tube-launched scramjet-powered hypersonic cruise missile. The key common features of both these types of hypersonic missile systems are their very high speed over long range, giving the target little time to react or evade, as well as the ability to maneuver in flight so as to complicate any attempt to track and intercept the warhead or warheads.
The Japanese Maritime Self-Defence Force, Japan’s Navy, has neither the necessary submarines nor hypersonic missiles in service yet, so the budget intent is likely to have a long gestation before the capability can be delivered. The Asia Times notes that Japan has previously described development work on both types of system: the Type 25 hyper-velocity gliding projectile system, with its Block 2B version having a planned range of 1,620nm “at Mach 5 and faster,” and a less advanced project to build a scramjet-powered hypersonic cruise missile.
The latest attack submarine that Japan is deploying is the Taigei Class, which is equipped with 6 533 mm torpedo tubes and thus can already launch subsonic cruise missiles such as the Harpoon UGM-84. Japan has up to now commissioned five Taigei Class submarines, the latest being JS Ch?gei (SS-517), which was launched in March 2026. The Taigei Class was designed from the start to be an operational test bed for the development of new and improved technologies, and each succeeding launch is of an upgraded variant. Incorporating vertical-launch tubes into the Taigei profile is probably a stretch too far however, and Kawasaki Heavy Industries have been working on a new design for a diesel-electric attack submarine since December 2023. Notwithstanding Japan’s constitutional limitations, the Japanese Defense Minister Shinjir? Koizumi has openly discussed the need for Japan to have nuclear-powered submarines, which if adopted would mean the future design with vertical launch tubes would conceptually look very similar to that being developed by AUKUS.
Kim Jong Un inspects an 8,700-ton submarine under construction, December 2025 (Korean Central News Agency)
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Japan’s Prime Minister Sanae Takaichi was elected with an unusual super-majority on a platform for radically strengthening Japan’s defense posture, being faced with rising threats from China, Russia and North Korea. The drive for submarine-launched hypersonic weapons has particular relevance to the threat posed by North Korea’s growing nuclear arsenal – and the likelihood that North Koreas is attempting to develop a submarine-launched nuclear ballistic missile threat.
North Korea’s Dear Leader Kim Jong Un has already been seen inspecting an 8,700-ton submarine under construction, with analysts unclear whether it is nuclear-powered or has vertically-launching missile tubes in the dorsal fin which looks large enough for the purpose. There is concern in Japan and South Korea that assistance in developing this capability has been the price paid by Russia for North Korean help in the war against Ukraine, cooperation that could end up with North Korea being able to launch a ballistic missile with a nuclear warhead from a long-range nuclear-powered submarine.
