Japan and the U.S. Validate Alliance Rear Support in Anticipation of Major Nankai Trough Earthquake during JXR26

The first thing that caught my attention in the announcement from the U.S. Indo-Pacific Command out of Yokota Air Base was not the names of ships or aircraft, but the term "last tactical mile" related to rear support. From July 20 to 24, the U.S. military and the Japan Self-Defense Forces conducted the Joint Exercise Rescue 2026. The scenario involved a major earthquake and tsunami in the Nankai Trough, with the affected area being the Kinki region, compounded by infrastructure collapse, disruption of lifelines, and numerous casualties under extreme heat.

Alliance Operations Seen as Disaster Exercises

On the surface, this was a humanitarian assistance and disaster relief (HA/DR) exercise. However, for those familiar with the workings of the Japan-U.S. alliance, JXR26 was not merely a rescue training. The U.S. military took on a supporting role, while Japan's Ministry of Defense maintained the lead in response. This structure is also applicable to operations in rear areas during emergencies. If a large-scale disaster occurs within Japan, ports, airports, fuel, medical services, roads, and communications would be simultaneously strained. In a situation where tensions rise in the southwestern region or around the Korean Peninsula, the same infrastructure would also be required for defense operations.

Validated Capabilities

• The duration was five days from July 20 to 24, 2026.
• The participating framework included the U.S. Forces Japan and the Joint Staff Office of the Self-Defense Forces.
• Key items included medical support, complex evacuation coordination, ongoing life support, and transition to hygiene management.
• In terms of communications, the emphasis was placed on procedures for Japan and the U.S. to accurately share the same information under rapidly changing crisis conditions.

According to the U.S. announcement, U.S. Forces Japan Commander Lieutenant General Stephen Jost stated that they conducted a stress test of the coordination mechanism to ensure a rapid and effective response between Japan and the U.S. during a real disaster. Additionally, Colonel Christopher Kim, in charge of logistics, explained that a plan to connect logistics from the operational area to the last tactical mile is necessary. This pertains not only to relief supplies but also to ammunition, fuel, medical transport, and port reopening.

The Nankai Trough as the Alliance's Rear Front

The Cabinet Office's Working Group on Measures for Major Earthquakes in the Nankai Trough has been examining estimates of human, material, and economic damage. While there is a range of assumptions regarding specific figures, the expectation of large-scale damage spanning from Kinki to Tokai, Shikoku, and Kyushu remains unchanged. From the perspective of the Japan Maritime Self-Defense Force, this is a crisis occurring within the defense of SLOC (Sea Lines of Communication). If ports and air bases on the Pacific side are simultaneously damaged, the Japanese archipelago, which supports the forward deployment of U.S. forces, itself becomes a logistical constraint.

What is important here is that JXR26 was conducted as training with the Joint Staff Office of the Self-Defense Forces. The attempt to unify communication lines with the U.S. military, transcending the divisions among land, sea, and air forces, cannot function solely through institutional reforms on paper. Even in the case of medical transport, factors such as the nationality of patients, receiving hospitals, legal responsibilities, and aircraft operational permissions come into play. It is candid that Colonel John Cotton of the U.S. Air Force acknowledged that coordination of medical policies between Japan and the U.S. has been a challenge in past real disasters.

Relation to Deterrence

Deterrence against China and North Korea cannot be established merely by the number of F-35s or Aegis ships. When bases are damaged, roads are cut off, and civilian evacuations and troop movements compete for the same routes, the alliance is truly tested for speed. The value of JXR26 lies in the fact that, while it was an exercise not focused on an enemy, it measured the vulnerabilities of the alliance that adversarial nations pay the most attention to, namely, the fragility of the rear.

In my view, the focus of JXR26 was not a tale of rescue capabilities. The question was how well Japan could lead and the U.S. could support in the fields of communications, medical care, and logistics.

During the Cold War, Japan could relatively static consider its role as a rear base. Japan in 2026 is different. The Nankai Trough, the Taiwan Strait, the Korean Peninsula, and cyberattacks could overlap rather than occur in a time-lagged manner. The unresolved risks highlighted by JXR26 are not due to a lack of equipment, but rather conflicts in priorities, including civilian infrastructure. Who decides which lives to save during a disaster and which units to mobilize for deterrence, based on what information and within what timeframe? There lies the quietest weakness of the alliance.

Main Sources

• U.S. Pacific Command, USFJ, JSDF stress-test bilateral disaster relief capabilities during JXR 26, 29 July 2026.
• Cabinet Office Disaster Prevention Information, Materials from the Working Group on Measures for Major Earthquakes in the Nankai Trough.