The project is part of Japan’s FY2027 defence budget request. The aim is to give Japan another way to launch long-range missiles from submarines that are hard to detect.   Japan’s Ministry of Defense included the plan in its FY2027 budget request released at the end of August 2026.   The request also includes about ¥48 billion ($325 million) to study an underwater vertical launch system, or VLS, for larger long-range missiles on Japan Maritime Self-Defense Force (JMSDF) submarines.   Japan is also studying a missile launch system for unmanned underwater vehicles, or UUVs.   China has improved its satellites, surveillance systems, missiles and air forces. These systems can threaten Japanese air bases, naval facilities and known missile sites.   Land-based missile units can move. Warships can also change position. But both can still be tracked by satellites and other surveillance systems.   Submarines are harder to find when they are underwater. Their exact location can remain unknown while they move toward a launch area.  This could help Japan keep some long-range weapons available even after an enemy attack on its military bases.   Finding a submarine after it launches a missile would also be difficult. An enemy could have to search a large area of sea using submarines, anti-submarine aircraft, warships and underwater sensors.

Japan has not said how far the new missile will travel. It has also not given details about its size, propulsion system or warhead.   The ¥48 billion VLS research could allow future JMSDF submarines to carry larger long-range missiles.   Japan’s current submarines use torpedo tubes to launch weapons. The Taigei-class submarines have six 533 mm torpedo tubes and can launch weapons such as the Harpoon UGM-84.     Torpedo tubes limit the size of a missile.   A VLS could provide larger launch cells. It could also give missiles more room for propulsion and possibly allow them to travel farther.   At the same time, the torpedo tubes could remain available for anti-submarine and anti-surface warfare.      Japan will need to study how the VLS can work safely underwater. This includes the structure of the launch system, how the missile leaves the submarine and how the launch affects the submarine’s stability. Japan also wants to study a missile launch module for UUVs. Tokyo has not said how large these UUVs would be, what missiles they would carry or how the launch system would work.   There is also no indication that the planned hypersonic missile itself would be carried by a UUV.   In the future, UUVs carrying missiles could give Japan more launch positions without putting submarine crews at risk.      They could also make it harder for an enemy to find all of Japan’s underwater weapons.   The submarine missile plan is part of Japan’s effort to build stand-off weapons.   Japan is improving its Type 12 surface-to-ship missile family. It is also working on hypersonic and other high-speed weapons. Japan is acquiring U.S.-made Tomahawk cruise missiles and other air-launched stand-off weapons. It is also looking at a cheaper stand-off weapon to work alongside more expensive systems.   Hypersonic missiles are likely to cost more and be available in smaller numbers. They could be used against important targets where speed is important.   Cheaper missiles could be used in larger numbers and for longer operations.   The submarine will also need accurate information about its targets.      Japan is investing in space-based surveillance, sensor networks, AI-based satellite data processing and communications systems for stand-off weapons.  This is important because targets such as warships can move.      A submarine could be hundreds of kilometres from its target and remain hidden. It cannot track every target from that distance on its own.   Japan could use information from satellites, maritime patrol aircraft, surface ships, unmanned aircraft and other systems. This would allow the submarine to stay hidden while receiving information from other platforms.   The same system could help Japan and the United States keep using long-range weapons if some air bases, ships or land-based launchers are damaged.   If the VLS program moves ahead, future JMSDF submarines could have more long-range strike missions.

They could still be used for anti-submarine warfare, intelligence gathering and attacks on surface ships.

They could also carry long-range missiles for targets such as command centres, missile batteries, air-defence systems and naval facilities.    The Taigei class is Japan’s latest attack submarine class. Japan has commissioned up to five submarines in the class.

The latest boat, JS Chōgei (SS-517), was launched in March 2026.   The Taigei class was also designed to test new technologies, with later boats receiving improvements.   Kawasaki Heavy Industries has been working on a new diesel-electric attack submarine design since December 2023.

Japanese Defence Minister Shinjirō Koizumi has also discussed the need for nuclear-powered submarines.