The concept of sea power, proposed by Alfred Mahan, was aimed initially at the exclusive control over sea lanes and areas vital to a nation’s interest or operations. However, sea power is now being transformed into a diplomatic tool, with its ability to provide a "free and open ocean" seen as a safe public good, maintained through international order, that contributes to confidence building and deterrence of armed conflicts. Considering the upheaval in the maritime order in recent times, what kind of influence does sea power wield, and what strategic roles are expected of it?

The Three Strategic Documents (National Security Strategy, National Defense Strategy, and Defense Buildup Program), approved by the Cabinet in December 2022, maintain Japan's existing security policies while clearly stating the intent to make changes and advancements on a practical level by maximizing Japan's comprehensive national power, including diplomacy, defense, economy, and information technology. The first National Security Strategy was approved by the Cabinet in 2013. However, significant changes in the security environment surrounding Japan, including the invasion of Ukraine by Russia, a permanent member of the UN Security Council, played a large role in leading to the 2022 revision.
The Indo-Pacific region, including Japan, is no exception to change, and structures of conflict exist, such as the rivalry between the US and China. Meanwhile, the region generates about 60% of the world's GDP and is complex, where countries with various political systems and geographical conditions are located. Given these circumstances, not only coastal nations in the region, but European countries are also actively increasing their engagement with the Indo-Pacific.

The concept of sea power, proposed by Mahan in "The Influence of Sea Power upon History" (1890), is not strictly defined. However, his academic contribution lies in theorizing that sea power is fundamental not only for overseas trade, logistics, and colonial acquisition but also for securing control of the seas in historical struggles for hegemony. Julian Corbett, in "Some Principles of Maritime Strategy" (1911), also pointed out the importance of securing sea lines of communication (SLOCs). In other words, when the concept of sea power began to be organized, its goal was the exclusive control of sea lanes and areas vital to a nation’s interests or operations.
However, over time, sea power has evolved from control of the seas or exclusive use of maritime areas to maintaining a "free and open ocean" as a safe public good under the existing international order, which serves as a diplomatic tool for confidence building and deterrence of armed conflicts. One factor that accelerated this change and formed the existing international order were the activities of the United States since the 20th century, which has helped maintain world order. After World War II, it cannot be ignored that the United States, which inherited maritime supremacy from the United Kingdom, positioned the oceans as a public good and aimed to maintain a peaceful and stable maritime order based on the rule of law.
On the other hand, unilateral attempts by certain countries to change the status quo, such as in the South China Sea, cannot be overlooked. Creating a stable security environment is essential to prevent the situation from worsening or threats being actualized. For this, maintaining strong communication among the parties involved is an absolute necessity. For decades, Japan has supported consultations among the parties involved in various international issues in the Indo-Pacific region as well as the processes that lead to the actual building of cooperative relationships. The core of this support has been diplomatic and security-related initiatives, but the premise is mutual support and trust, with frameworks for conflict deterrence and peaceful resolution being implemented additionally or incrementally.

What influence does sea power have on the confidence building and conflict deterrence needed to solve these issues? In the Indo-Pacific region, attention is being paid not only to territorial disputes in the South China Sea but also to the peace and stability of the Taiwan Strait. Properly managing these conflicts and tensions and preventing accidental incidents is an urgent matter. If mutual understanding through dialog among parties and transparency through information disclosure can be achieved, and if agreements can be reached on various initiatives, confidence-building measures, including defense exchanges, can be established. For example, in the Japan Maritime Self-Defense Force, efforts to secure concrete transparency begin with personnel exchanges and develop into mutual visits of naval ships.
On the other hand, deterring armed conflicts strongly demands that the intent of entities considering invasion or preemptive military action be addressed. The basic idea of deterrence is to make the other party recognize that the risks and costs resulting from using force will have significant negative impacts in the long run, thus dissuading them from taking action. Today, the United States is still the world's largest sea power and is an ally of Japan. The United States, in cooperation with Japan and other allies, continues to form and maintain maritime order based on the rule of law and provide it as a public good. However, due to changes in the balance of power and political leadership fluctuations in the international community, it is becoming increasingly difficult for international unity to function as an effective deterrence. Strengthening alliances and messaging that shares universal values are effective ways to improve this situation. Also, recognizing that the stabilizing of regional societies is also important, broadly defining sea power as an option for providing support to developing countries seeking a broad range of aid rather than just military-focused support is also effective, in addition to strengthening governance from outside the region.

Attempts by nations or groups that do not share universal values to unilaterally change the status quo to secure their own exclusive interests must not be tolerated. Creating a stable security environment must, therefore, be the top priority. Sea power, with its highly flexible and international nature, is a concept that has been defined both frequently and broadly. Nevertheless, in terms of contributing to the prosperity of a nation and its surrounding regions, Mahan's definition of sea power remains relevant and practical today. Thus, all in the international community should equally recognize the effective functioning of sea power, which includes the narrow sense of naval power that supports diplomatic and security policies. For this reason, in defense exchanges with relevant countries, building large, robust, and multilayered connections with allied and like-minded nations that contribute constructively and stably to sea power is increasingly essential, thereby enhancing deterrence. I believe the strategic role of this concept in peacetime will be even more crucial in the future.