Introduction
In recent years, amidst rapid changes in the international situation, the question of whether Japan's defense capabilities are sufficient has been debated in various sectors of society. Of particular interest is the issue of nuclear submarines. The Liberal Democratic Party and the Japan Innovation Party have reached an agreement to promote a policy of acquiring VLS-equipped submarines utilizing next-generation propulsion systems, but is this decision truly correct?
This article features an interview with Yoji Koda, former commander of the Japan Maritime Self-Defense Force's Self-Defense Fleet, delving into the necessity and role of introducing nuclear submarines. While explaining technical terms in an easy-to-understand manner, we present the current defense strategy and future possibilities through three scenarios.
By reading this article, you will understand "why nuclear submarines are a hot topic now," "whether they are truly necessary," and "what role they play." This content will be useful for those interested in national security, or for those whose work involves paying attention to international affairs and technological trends.
Nuclear submarines "don't need to be introduced right now, but their future potential should be considered."
According to Yoji Koda, former commander of the Japan Maritime Self-Defense Force Fleet, in Japan's current defense conceptnuclear submarineIt is not considered essential. However, the conclusion is that it is necessary to consider future changes in the security environment, technological advancements, and environmental issues.
The essence of this discussion lies in the idea that, rather than outright rejecting nuclear propulsion, we should consider submarine propulsion methods, including their future potential. In other words, while immediate implementation isn't necessary, the strong implication is that technological development and research should be pursued with a long-term perspective.
Why is this discussion attracting attention now?
In September 2025, a report compiled by an expert panel on fundamentally strengthening defense capabilities recommended that "necessary research should be conducted regarding VLS-equipped submarines, including consideration of utilizing next-generation propulsion systems." This sparked simplistic interpretations such as "nuclear submarines should be introduced immediately" and debates about whether it was related to nuclear armament.
However, experts generally believe that the immediate introduction of nuclear submarines is not essential for current defense capabilities, and that we should first focus on higher-priority issues such as measures to address the declining birthrate and the development of unmanned technologies.
Specific details
Point 1: The role of current diesel submarines
Currently, the Japan Maritime Self-Defense Force's newest submarine is a diesel-powered type called "Sogei." This submarine is responsible for the following roles:
Strait monitoring: Stationed around the Soya Strait, Tsugaru Strait, Tsushima Strait, Miyako Strait, and Bashi Channel.
Surveillance mission: Monitoring to prevent Chinese and Russian submarines from entering the Pacific Ocean.
Prioritizing quiet operation: The sound during submersion is quiet and difficult to detect.
Diesel submarines are superior for surveillance activities, especially in straits, because the ability to "wait quietly" is more important than high speed. Nuclear submarines excel at high-speed movement, but they are not necessarily suited for standby missions.
Point 2: Three future scenarios and the potential of nuclear submarines
The following three scenarios are considered to be the main ones in which nuclear submarines may be needed in the future:
Scenario 1: Role: Destroying a Chinese aircraft carrier strike group
Currently, China has three aircraft carriers in service, and more are expected to be added in the future. The United States also has five carrier strike groups deployed in the Pacific. There is a possibility that the aircraft carriers of both countries will cross the first island chain and face off in the Western Pacific, and in order to create a stalemate that would be advantageous to Japan and the United States, a plan to "sink Chinese aircraft carriers" is being considered.
If two ships were sunk, it would inflict a tremendous psychological blow on China. The idea is to have nuclear submarines play this role. However, in actual speed comparisons:
China's aircraft carrier Fujian: approximately 30 knots
Japan Maritime Self-Defense Force's latest diesel submarine (Sogei): Maximum speed of approximately 18 knots while submerged.
Nuclear power is necessary to bridge this gap, but diesel engines are also viable if the fleet is waiting in straits around the Southwest Islands.
Scenario 2: Used as a means of transporting standoff missiles
A "standoff missile" is a long-range, precision-guided missile launched from outside the enemy's range. After attacking from a submarine, the launcher must quickly leave the area because their position would be revealed to the enemy the moment they fired.
For example, to attack a Chinese naval base on Hainan Island, the standoff missiles would need to travel as far southwest as Taiwan before reaching their target (approximately 1000 km). Current diesel submarines face the risk of nearly half being destroyed after firing. Such high-risk operations may eventually be handled by unmanned submersibles.
Scenario 3: Strengthening surveillance of the Arctic Ocean
Currently, the attention of countries around the world is focused on the Arctic Ocean. Due to the effects of global warming, sea ice is decreasing, expanding the routes and periods in which warships can navigate. Russia, in its maritime doctrine published in 2022, designated the Arctic Ocean as a "critically important sea area," and seabed resource development is also becoming more active.
The need to strengthen surveillance of the Soya Strait and Tsugaru Strait is increasing, so it is necessary to consider increasing the number of submarines and improving their speed. However, there is a practical challenge in that this will depend on the number and skills of crew members that can be secured.
Point 3: What is "power"? The potential of SMR
The term "nuclear power" is often used in discussions, but it's important not only in the sense of a propulsion system, but also in the sense of providing the electricity to power defense equipment.
In the future, the use of small modular reactors (SMRs) may become essential. For the Japan Maritime Self-Defense Force, which is responsible for combat at sea and underwater, far from land-based power sources, nuclear power is more of a "power source" than a "propulsion system."
Point 4: Challenges and costs associated with implementation
If nuclear submarines are to be introduced, the following challenges will arise:
Disposal of radioactive waste: Managing it "from cradle to grave" is extremely difficult.
Securing Crew: Can the Self-Defense Forces, facing a shortage of personnel, secure skilled pilots?
Power Consumption: The introduction of missile-carrying unmanned platforms will consume more power than current submarines.
To solve these challenges, it is necessary to proceed not only with technological development, but also with human resource development and infrastructure improvement in parallel.
What does "next-generation power" refer to?
The term "next-generation propulsion" in discussions related to "VLS-equipped submarines" does not simply mean nuclear propulsion. In the future, it may also include the following technologies:
Small modular reactors (SMRs): Enable independence from onshore power sources.
Hybrid system: Combining diesel and nuclear power
Collaboration with unmanned platforms: such as unmanned missile launch platforms.
These are concepts that differ from the conventional idea of "nuclear power promotion." The Ministry of Defense's expert panel report also uses the phrase "rather than outright rejecting nuclear power promotion," indicating that a flexible approach to technological selection is required.
Consistency with current defense concepts
Current Japanese defense strategies do not require nuclear submarines. However, long-term consideration is necessary to respond to changes in the international situation and technological advancements. The following points, in particular, should be considered:
1. Clarify priorities: Measures to address the declining birthrate and automation technologies have a more immediate impact.
2. Phased implementation: Research and development will proceed in parallel, rather than immediately.
3. Flexible options: Consider not only nuclear power but also other propulsion methods.
Explanation of technical terms
Here's a brief explanation of the main technical terms used in this article:
- VLS (Vertical Launch System): A missile launch system equipped on surface ships and submarines.
- Standoff missile: A long-range precision-guided missile launched from outside the enemy's range.
- SMR (Small Modular Reactor): A small modular reactor. Smaller and more flexible design than conventional nuclear power plants.
- Knot: A unit of speed at sea. 1 knot = approximately 1.85 km/h
Understanding these points will allow you to better understand the article's content, but no specialized knowledge is required.
Summary
Defense strategy is "preparation for future uncertainties."
What this article has made clear is that the seemingly simple issue of "introducing nuclear submarines" actually involves multi-layered and complex challenges. It's not simply a matter of "wanting or not wanting," but rather needs to be considered within the context of "when," "under what circumstances," and "what role will they play."
In Japan's current defense strategy, nuclear submarines are not immediately necessary. However, the implication is that they should be considered in light of future changes in the security environment, technological advancements, and environmental issues.
Work-related insights: The balance between "doing what to do now" and "preparing for the future"
This discussion offers important lessons for work and project management:
- Clarifying priorities: Determining what to prioritize with limited resources.
- Maintaining a long-term perspective: Consider not only short-term gains but also future possibilities.
- Offer flexible options: Don't stick to one solution, consider multiple approaches.
Nuclear submarines are a symbolic representation of this balance. While there is no immediate need to introduce them, pursuing technological development and research in parallel will allow us to prepare to respond to future changes in the security environment.
Key points to watch out for in the future
The following points will likely attract attention going forward:
- Details of the expert panel's report: Specific contents of the September 2025 report
- Technological advancements: Practical application of SMRs and unmanned platforms.
- Changes in the international situation: particularly the military developments of China and Russia and the situation in the Arctic Ocean.
As we closely monitor these developments, how Japan's defense strategy evolves remains a topic we should continue to pay attention to.
