Keen Sword 27: US-Japan Military Exercise Begins (Oct 19-29)

Keen Sword 27 — the largest Japan–U.S. joint military exercise of 2026 — began on Monday, October 19, 2026, and runs through Thursday, October 29 across Japan. The biennial drill brings roughly 45,000 Japan Self-Defense Forces personnel together with U.S. forces for island-defense training, with a headline first: the U.S. Marine Corps is deploying its NMESIS anti-ship missile system to Yonaguni, Japan's westernmost island, about 110 kilometers from Taiwan.

Keen Sword 27: Scale and Schedule

According to the Japan Joint Staff press release issued September 29, 2026, Keen Sword 27 is the 18th iteration of the bilateral exercise series, held every other year in alternation with the Keen Edge command-post exercise. The official figures are striking:

U.S. participation figures have not been publicly released, but forces from all U.S. services in the Indo-Pacific and units based in Japan are taking part. The previous iteration, Keen Sword 25, involved about 33,000 Japanese personnel and 12,000 U.S. personnel, making this year's edition a significant step up.

The Yonaguni First: NMESIS Near Taiwan

The most closely watched element of Keen Sword 27 is the first-ever deployment of the U.S. Marine Corps' Navy-Marine Expeditionary Ship Interdiction System (NMESIS) to Yonaguni Island. Yonaguni is Japan's westernmost inhabited island, sitting roughly 110 km east of Taiwan at the end of the Ryukyu chain. NMESIS previously operated from Ishigaki during 2025 joint training; its move to Yonaguni shifts American expeditionary anti-ship capability farther west, closer to waters surrounding Taiwan. The short-range air-defense system MADIS is also expected to deploy alongside it, and NMESIS will return to Ishigaki during the exercise as well.

What the Exercise Will Train

The official exercise program lists an unusually broad set of training events, reflecting the multi-domain nature of modern conflict:

• Integrated air and missile defense and bilateral joint offensive anti-ship operations
• Ground, maritime, and air operations, plus amphibious operations training
• Cyber attack response and information warfare training
• Joint electromagnetic warfare and space domain awareness
• Agile combat employment, distributed operations, and critical infrastructure protection
• Joint logistics and communications drills

Training will take place at JSDF and U.S. military facilities, civilian airports and ports, public and private land, and the sea and airspace surrounding Japan. Notably, Osprey aircraft have already been seen operating from civilian airports at Miyako and Ishigaki in the lead-up to the exercise, a point raised in Japan's October 16 defense minister press conference.

Allies Join In

Beyond the U.S.–Japan core, seven allied nations are participating: Australia, Canada, France, Germany, the Netherlands, New Zealand, and the Philippines. Their involvement underscores how the exercise doubles as a signal of collective commitment to regional stability in the Indo-Pacific.

The Bigger Picture: Why It Matters Now

The timing is charged. Just days before the exercise opened, China's aircraft carrier Liaoning sailed into the western Pacific on October 14 for training described by Beijing as routine — its second western Pacific deployment of 2026. Chinese maritime authorities also closed five zones across the Bohai, Yellow, East China, and South China Seas for exercises from October 12–17. Analysts at outlets like Defense War Room note the dense calendar as the exercise opens. For background on the broader security landscape, see our coverage of Iran's underground missile cities and recent U.S.–China talks. Official details are available in the Japan Joint Staff press release (PDF).

Conclusion

Keen Sword 27 is more than a routine drill — its expanded scale, the debut of NMESIS on Yonaguni, and the participation of seven allied nations make it the clearest indicator yet of how the U.S.–Japan alliance is preparing for contingencies in the southwestern islands. With the exercise running through October 29, expect daily developments, and check back for updates as training events unfold.