Regional Security: What Could Japan Learn from the U.S. – Philippine Mutual Defense Treaty of 1951?

Article by John Carlo T. Seralbo

February 12, 2023

The Japan Maritime Self-Defense Force is rising as a potential regional security leader alongside the United States in the Asia-Pacific region. It has the military capability to secure peace alongside U.S. military assets in the area such as those in Kadena Air Force Base and Yokosuka, the home of the U.S. 7th Fleet. It could also have the ability enforce the freedom of navigation of vessels on international waters under the United Nations Convention on the Law of the Sea. However, in today’s Japan in which about three quarters of the population are worried of a foreign attack, according to a survey by Japan Press Research Institute, how is the United States likely to respond to a hypothetical armed threat against Japan in the region? Article V of the Treaty of Mutual Cooperation and Security Between Japan and the United States states that: "Each Party recognizes that an armed attack against either Party in the territories under the administration of Japan would be dangerous to its own peace and safety and declares that it would act to meet the common danger in accordance with its constitutional provisions and processes."

Here, it seems clear that an attack within Japanese territory would trigger U.S. action to meet the common danger, but what about those outside its jurisdiction, such as when a Japanese Maritime Self-Defense vessel is patrolling outside its territorial waters? Such an attack was portrayed in the Korean movie “Steel Rain” where a Japanese Aegis was struck by a missile in the East Sea outside of the Japanese contiguous zone. Perhaps the Japanese government could learn something by comparing the U.S. – Japanese security agreement against the U.S. – Philippine Mutual Defense Treaty of 1951, where it can be seen that slight difference in wording seems to make the difference in determining the answer to the question of U.S. response. Article IV of the U.S. – Philippine Mutual Defense Treaty of 1951 states that:

Each Party recognizes that an armed attack in the Pacific area on either of the Parties would be dangerous to its own peace and safety and declares that it would act to meet the common dangers in accordance with its constitutional processes.

Although both the U.S. – Japan and U.S. – Philippine treaties sounds almost the same, the latter includes “the Pacific area.” Consequentially, this slight difference in wording shaped the Philippines’ security policy beyond its territorial sea. In the heightened fear of U.S. withdrawal in the Pacific after the United States pulled out of Vietnam in 1975, the Philippines asked the United States to clarify what constitute the Pacific under the U.S. – Philippine Mutual Defense Treaty. For instance, a November 23, 1976 telegram from the U.S. Secretary of State to the American Embassy in Manila shows that Carlos P. Romulo, the Philippine Minister of Foreign Affairs of that time, asked Kissinger, stating:

"We would like to have a more precise definition of the term ‘Pacific area.’ For example, would the South China form part of the Pacific area? From our point of view, we believe the South China Sea should be included in the Pacific area."

The United States eventually clarified in 1978 through a formal diplomatic letter stating that an attack on Philippine vessels in the Pacific, including the South China Sea, would result in a U.S. response under the Mutual Defense Treaty of 1951. Fast forward today, this interpretation of the Pacific area remains, where U.S. officials constantly affirms publicly that an armed attack against the Philippines would trigger the U.S. – Philippine Mutual Defense Treaty.

What does this mean for Japan? From a purely strategic point of view, a defense treaty with the United States which would encompass areas beyond Japanese immediate territorial waters, much like the U.S. – Philippine Mutual Defense Treaty of 1951, would potentially result in an increased deterrence capability of the Japanese Navy against threats in the region’s stability and peace, enhancing Japan’s role as a regional security force. Of course, this is under the assumption that Japan would want to take that path.

*The information provided does not, and is not intended to, constitute legal advice.