Japan’s Hypersonic Submarine Missiles: A Mach 5 Game-Changer in the Pacific
Japan’s FY2027 defence budget allocates $325m to develop underwater-launched hypersonic missiles capable of Mach 5.
Japan has unveiled plans to equip its submarines with hypersonic missiles, a move aimed at countering North Korea’s growing nuclear arsenal and China’s military expansion in the Pacific. The FY2027 defence budget request, presented by Prime Minister Sanae Takaichi, allocates ¥48 billion ($325 million) for research into an underwater-launched hypersonic missile system capable of firing missiles at Mach 5 or faster.
The initiative marks a significant escalation in Japan’s defence strategy, as the Japanese Maritime Self-Defence Force (JMSDF) currently lacks both the submarines and hypersonic missiles required for such a capability. The budget request describes the weapon as an “underwater-launched,” “high-survivability missile” that can strike “at an early stage and at long range,” a direct response to the evolving threats in the region.
Why Hypersonic Missiles? The Strategic Imperative
The decision to pursue hypersonic technology stems from the missile’s two defining advantages: speed and manoeuvrability. Hypersonic missiles travel at least five times the speed of sound, leaving targets with little time to react or intercept. Their ability to change course mid-flight further complicates defence efforts, making them a critical asset in modern warfare.
Japan’s defence planners are considering two types of hypersonic systems: a vertically-launched ballistic missile and a torpedo-tube-launched scramjet-powered cruise missile. Both variants would be derived from the Type 25 Hyper Velocity Gliding Projectile (25HGP), a system already in development with a planned range of 1,620 nautical miles. The Block 2B version of the Type 25, with a planned range of 1,620 nautical miles at Mach 5 and faster, offering a formidable strike capability.
The urgency of Japan’s hypersonic programme is underscored by North Korea’s advances in submarine-launched ballistic missile (SLBM) technology. In December 2025, North Korean leader Kim Jong Un inspected an 8,700-ton submarine under construction, sparking concerns in Tokyo and Seoul. Analysts remain divided over whether the vessel is nuclear-powered or equipped with vertical missile tubes, but its sheer size suggests a potential platform for nuclear strikes.
The Submarine Gap: Japan’s Race to Catch Up
Japan’s current submarine fleet, led by the Taigei Class, is ill-equipped for hypersonic missile deployment. The Taigei Class, which includes five commissioned vessels with the latest being JS Chōgei (SS-517) launched in March 2026, features six 533 mm torpedo tubes capable of firing subsonic cruise missiles like the Harpoon UGM-84. However, these tubes lack the capacity to launch larger, long-range hypersonic weapons.
To bridge this gap, Kawasaki Heavy Industries has been developing a new diesel-electric attack submarine design since December 2023. The future submarine is expected to incorporate an underwater-launched hypersonic missile system, a feature that would align Japan’s capabilities with those of the AUKUS partnership, Australia, the UK, and the US, which is also pursuing nuclear-powered submarines with vertical launch tubes.
Japanese Defence Minister Shinjirō Koizumi has openly discussed the need for Japan to acquire nuclear-powered submarines, a move that would require a significant shift in the country’s post-war defence posture. While Japan’s constitution currently limits its military to self-defence, the growing threats from North Korea, China, and Russia have prompted a re-evaluation of these constraints.
The FY2027 budget request also includes JPY14.2 billion ($89 million) for continued development of hypersonic guided missiles and JPY167.3 billion for the acquisition of hypersonic missiles and associated ground equipment. These investments reflect Japan’s commitment to closing the technological gap with its adversaries and ensuring its forces can operate effectively in contested environments.
For Japan, the stakes could not be higher. North Korea’s collaboration with Russia, reportedly in exchange for military assistance in Ukraine, has raised fears that Pyongyang could soon field a submarine capable of launching nuclear-tipped ballistic missiles. Such a development would dramatically alter the security landscape in the Pacific, forcing Japan to accelerate its own military modernisation efforts.
The hypersonic missile programme is not just about deterrence, it is about survival. With China expanding its naval presence in the East China Sea and Taiwan Strait, and North Korea’s nuclear ambitions growing bolder, Japan’s leaders see hypersonic weapons as a necessary countermeasure. The ability to launch high-speed, manoeuvrable missiles from concealed underwater platforms would give Japan a critical edge in any potential conflict, allowing it to strike quickly and evade enemy defences.
As the programme progresses, the JMSDF will need to overcome significant technical challenges, including the integration of vertical launch systems into its submarines and the development of reliable hypersonic propulsion. The road ahead is long, but Japan’s defence planners are betting that the investment will pay off in the form of a more secure and stable Pacific region.
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