Japan Proposes Submarine-Launched Mach 5 Hypersonic Missile in 2027 Budget to Challenge China in Pacific.

Japan has proposed developing a submarine-launched hypersonic guided missile capable of exceeding Mach 5, potentially giving Tokyo a harder-to-detect long-range counterstrike option as China expands its missile, naval, and air power. Included in Japan’s FY2027 defense budget request, the project would strengthen the survivability of Japanese strike forces by allowing future weapons to operate from concealed undersea platforms.

The proposal is paired with about ¥48 billion ($325 million) for research into an underwater vertical launch system able to accommodate larger long-range missiles aboard Japan Maritime Self-Defense Force submarines. Together, these technologies could extend Japan’s sea-based firepower and complicate an adversary’s ability to locate and neutralize its counterstrike assets.

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Japan’s FY2027 defense budget request includes development of an underwater-launched hypersonic guided missile and ¥48 billion ($325 million) for submarine vertical-launch-system research, potentially giving the JMSDF a more survivable long-range counterstrike capability. (Picture source: Japan MoD)

The Japanese Ministry of Defense disclosed the projects in its FY2027 budget request published at the end of August 2026, alongside research into a stand-off missile launch module for unmanned underwater vehicles. Together, the proposed investments indicate that Tokyo wants to develop an undersea strike architecture built around survivability, distributed launch positions and long-range precision fires, with potential implications for operations in the East China Sea, around Taiwan and across the wider Western Pacific.

The most important advantage would come before the hypersonic missile is ever fired. China has developed increasingly capable satellite surveillance, long-range reconnaissance, missile and air forces able to threaten fixed air bases, naval facilities and known missile positions across Japan. Land-based missile units can disperse and surface warships can maneuver, but both remain exposed to persistent surveillance. A submerged submarine presents a much harder targeting problem because its location can remain uncertain even while it moves toward a firing area.

That uncertainty could give Japan a more credible ability to retain counterstrike weapons after an initial wave of enemy attacks. Instead of relying primarily on visible launchers, aircraft sorties or surface combatants, Tokyo could keep part of its long-range arsenal underwater, forcing China to search large maritime areas using submarines, anti-submarine warfare aircraft, surface warships and undersea sensors. Even successful attacks against Japanese airfields and land-based missile positions would therefore not guarantee that Japan’s long-range strike capability had been suppressed.

Japan has not disclosed the planned range, dimensions, propulsion arrangement or warhead of the proposed underwater-launched missile. Its wider hypersonic weapons effort is based on speeds exceeding Mach 5, which can reduce warning and interception timelines once a weapon is in flight. Combining that speed with a concealed submarine launcher would create two separate challenges for an opponent: locating and tracking the firing submarine before launch, then detecting and intercepting the missile after it has been fired.

The proposed hypersonic missile is closely connected to Japan’s underwater vertical launch system research, with the FY2027 budget request identifying approximately ¥48 billion ($325 million) for the effort. A dedicated submarine VLS could substantially expand the strike role of future Japanese submarines because conventional torpedo tubes restrict missile dimensions and launch geometry. Vertical cells could accommodate larger stand-off weapons with more propulsion volume and potentially greater range while preserving torpedo tubes for anti-submarine and anti-surface warfare.

The VLS work includes pressure-resistant launch structures, missile launch performance and submarine stability during firing. Integrating a hypersonic weapon would add further demands because high-speed missiles require substantial propulsion capacity, thermal protection and advanced guidance. The central operational issue will therefore be how many long-range weapons a submarine can carry without reducing the acoustic discretion and sea-denial capabilities that make it valuable.

Japan’s FY2027 budget proposal also includes research into a stand-off missile launch module for an unmanned underwater vehicle, potentially adding another element to this distributed strike concept. Tokyo has not disclosed the size of the UUV, the missile type or the launch mechanism, and there is no indication that the proposed hypersonic missile itself will be carried by an unmanned underwater vehicle. Nevertheless, missile-armed UUVs could eventually create additional firing positions without placing submarine crews at risk and force an opponent to search for a wider range of underwater threats.

Together, the proposed submarine VLS, underwater-launched hypersonic missile, and UUV missile-module research would make the undersea environment increasingly important to Japan’s long-range strike strategy. Chinese anti-submarine forces could face the task of locating crewed submarines while monitoring unmanned underwater vehicles and simultaneously protecting naval formations, bases and other military targets from stand-off missile attacks.

The implications could become particularly significant during a Western Pacific crisis involving Taiwan. Japanese territory, especially the southwestern island chain, lies close to areas that would be strategically important during operations around Taiwan and the East China Sea. Airfields, ports, radar installations and missile positions in this region could become critical nodes for Japanese and U.S. forces, but their fixed locations also leave them vulnerable to long-range precision strikes.

Submarines carrying stand-off missiles would provide another way to preserve offensive firepower if those installations were damaged or temporarily disrupted. A Japanese submarine already at sea could remain concealed, reposition between firing areas, and continue threatening military targets without requiring access to an operational runway or an exposed land launcher. This could complicate Chinese planning by making it harder to determine how much Japanese strike capacity remained after the opening phase of a conflict.

The concept would introduce a conventional second-strike element into Japan’s defense posture. The objective is not simply to develop a faster missile, but to ensure that an adversary cannot confidently eliminate Japan’s ability to respond by attacking known bases and launch positions. The survival of missile-armed submarines would force an opponent to assume that command facilities, missile units, air-defense systems, naval bases and other military targets could remain exposed to counterattack.

Japan’s proposed undersea projects form part of a much larger stand-off weapons buildup. Tokyo is expanding the improved Type 12 surface-to-ship missile family, developing hypersonic and high-velocity weapons, acquiring U.S.-built Tomahawk cruise missiles and integrating additional air-launched stand-off weapons. FY2027 planning also includes a lower-cost stand-off weapon intended to complement more expensive high-performance munitions and deepen Japan’s missile inventory during prolonged operations.

That mix is operationally important because hypersonic missiles are likely to remain expensive and comparatively limited in number. Their speed and penetration characteristics make them better suited to high-priority, time-sensitive, or heavily defended objectives, while lower-cost stand-off weapons could provide the volume required for repeated attacks and saturation missions. A layered inventory would allow Japanese forces to reserve scarce hypersonic missiles for targets where Mach 5+ performance creates a decisive advantage.

The effectiveness of an underwater strike force will also depend heavily on Japan’s ability to detect and track targets at long range. Tokyo is investing in space-based surveillance, improved sensor networks, artificial intelligence-enabled satellite processing and communications supporting stand-off missile operations. These capabilities become particularly important against moving warships, where a submerged firing submarine could be hundreds of kilometers from the target and unable to provide continuous targeting information on its own.

This is where the proposed capability could become particularly important for U.S.-Japan operations. American and Japanese satellites, maritime patrol aircraft, surface warships, unmanned aerial vehicles and other intelligence assets could detect and track targets while a Japanese submarine remains concealed elsewhere. Separating the sensor from the shooter would allow the firing submarine to avoid revealing its position while creating additional strike axes across the Western Pacific.

In a conflict involving sustained missile attacks against Japanese and U.S. bases, this distributed arrangement could improve the resilience of allied long-range fires. Aircraft could face damaged runways, surface warships could be tracked, and land launchers would need to relocate repeatedly to survive. A submarine already operating beneath the sea could continue receiving targeting information from the wider allied network and retain a strike option even when other forces were under pressure.

For the Japan Maritime Self-Defense Force, submarine VLS could eventually broaden the mission of future submarines beyond anti-submarine warfare, intelligence collection and anti-surface warfare. Submarines equipped with vertical-launch stand-off weapons could contribute directly to conventional strikes against command centers, missile batteries, air-defense systems, naval facilities and other high-value military targets while continuing to threaten opposing ships and submarines.

Major technical and operational challenges remain, and the FY2027 request should not be interpreted as evidence that an operational submarine-launched hypersonic missile is imminent. Large vertical launch cells affect submarine hull design, displacement, internal arrangement, buoyancy and acoustic characteristics, while the missile must safely transition from underwater launch to high-speed atmospheric flight. Tokyo will also need to determine how many stand-off missiles future submarines can carry without weakening their traditional anti-submarine and sea-denial missions.

If the FY2027 projects progress into successful development and eventual deployment, however, their strategic consequence could extend well beyond another addition to Japan’s missile inventory. Combining Mach 5+ weapons, submarine vertical launch cells, lower-cost stand-off missiles and potentially missile-armed unmanned underwater vehicles could give Tokyo a concealed and distributed long-range strike capability designed to survive the opening phase of a major conflict.

For China, the central challenge would be uncertainty over where Japan’s underwater launchers are located and how many remain available after an attack. For the United States and Japan, the capability could add a more survivable element to combined operations across the Western Pacific by connecting allied surveillance and targeting networks with concealed underwater launchers. The FY2027 proposal therefore signals a potentially important shift in Japan’s counterstrike strategy: from simply increasing missile range toward ensuring that long-range firepower can survive, remain hidden, and still be used after the opening strikes of a regional conflict.

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Written by Alain Servaes – Chief Editor, Army Recognition Group
Alain Servaes is a former infantry non-commissioned officer and the founder of Army Recognition. With over 20 years in defense journalism, he provides expert analysis on military equipment, NATO operations, and the global defense industry.