Keen Sword 27: Japan and US deploy anti-ship missiles to islands near Taiwan

GRYD Indo-Pacific Watch

Japan and the United States began Keen Sword 27 on 19 October 2026, an 11-day exercise that Japan’s Joint Staff says involves about 45,000 Self-Defense Forces personnel. Japan’s Type 25 anti-ship missile is in an exercise for the first time, and US Marines are taking the Navy-Marine Expeditionary Ship Interdiction System (NMESIS) to Yonaguni, 110 km from Taiwan.

What we know

Japan’s Joint Staff Office (JSO) announced the exercise on 29 September. It is directed by Admiral Tateki Tawara, commander of Japan Joint Operations Command, and Admiral Stephen Koehler, commander of the US Pacific Fleet. The release lists 15 training areas, from air and missile defence and anti-ship combat to amphibious operations, cyber defence, space situational awareness and electromagnetic operations. It is the 18th field exercise in a series that began in Japan’s 1985 fiscal year.

The biggest first is the Type 25 surface-to-ship guided missile, which Defense News describes as the system formerly known as the upgraded Type 12. The Yomiuri Shimbun says it is being used in an exercise for the first time since it was deployed to Camp Kengun in Kumamoto, and will be moved to the Onohara training area in Nagasaki and Saga prefectures to rehearse targeting procedures without firing. A senior defence ministry official described it to Kyodo News as “symbolic” of Japan’s ability to strike enemy bases, which Tokyo officially calls counterstrike capability (our translation).

The US Marine Corps’ 12th Marine Littoral Regiment is deploying the NMESIS anti-ship launcher and the Marine Air Defense Integrated System (MADIS) to Yonaguni for the first time, Defense News and the Yomiuri report. The regiment received both on Okinawa in June. At sea, the carrier USS Theodore Roosevelt, the cruiser USS Chosin and the destroyer USS Decatur arrived at Yokosuka on 16 October “ahead of exercise Keen Sword”, the US Navy said.

Background

Keen Sword alternates with Keen Edge, a command post exercise, so the field version comes round roughly every two years (Kyodo). Its focus is the Nansei, or southwestern, island chain that runs from Kyushu to Yonaguni. Japan opened a radar and surveillance site on Yonaguni in 2016, Defense News notes, and has since added missile units along the chain, a shift covered in our analysis of how Japan is becoming a military power.

The US Marine Corps has reorganised in parallel around small island-based missile units. The NMESIS launcher at the heart of that effort is covered in our report on the Marines’ first NMESIS missile battalion.

Keen Sword 27 vs Keen Sword 25 at a glance

GRYD compared the Joint Staff Office announcements for the last two field exercises. Figures are official approximations; the 2026 US figure comes from press reports.

Where the missiles are going

Japanese defence ministry plans summarised by USNI News put ground-based missiles on at least four islands. Numbers are planned island detachments.

USNI News adds that the anti-ship and air and missile defence drills, south of Shikoku and in the East China Sea southwest of Kyushu, are not expected to involve live firing.

Why it matters

The first point is the shape of the exercise. In 2022 and 2024, a forward-deployed US carrier strike group headlined Keen Sword, USNI News notes. This year USS George Washington was sent to the Arabian Sea in August (Defense News), and it is the Theodore Roosevelt group that the US Navy says is preparing to join. The bigger change is ashore: mobile anti-ship and air defence launchers on islands from Tanegashima to Yonaguni, including Miyako, beside the passage the Liaoning group used on 14 October. In GRYD’s reading, that is a rehearsal for denying the sea to an enemy from land, not only for defending the islands.

The second point is Japan’s counterstrike policy. A missile with a reported reach of about 1,000 km, which Kyodo says would put parts of China’s coast in range, is now part of a bilateral drill, even if only for procedures. That makes Tokyo’s long-range strike plans a practical exercise question rather than only a budget line.

The third point is the wider coalition. Comparing the two Joint Staff releases, France, Germany, the Netherlands, New Zealand and the Philippines moved from the 2024 observer list to the 2026 list of foreign forces. USNI News says some will still only observe or join some drills, but a French frigate is due to practise boarding operations with Japan’s navy near Amami Oshima. The new training areas, from cyber defence to electronic warfare, suggest the allies expect a fight to start well before the first missile is fired.

What’s uncertain

• The full US order of battle. USNI News reported on 6 October that US details had not been released, and the Joint Staff release gives only Japanese numbers.
• Typhon. The US Army’s mid-range Typhon launcher is stored at Kadena Air Base on Okinawa, USNI News reports, but neither government has said whether it will take part.
• The Type 25’s real range. The 1,000 km figure comes from press reports, not an official specification.
• Local consent. Yonaguni’s local government remains opposed to the drills, and local officials say the exercise was scaled down from a larger plan (Defense News).

Around the Indo-Pacific this week

• China’s carrier crossed the island chain. Japan’s Joint Staff tracked the carrier Liaoning and three destroyers through the gap between Okinawa and Miyako on 14 October, with flight operations about 250 km south of Ishigaki. The group headed for the South China Sea on 15 October (JSO, 14 October; JSO, 15 October, in Japanese).
• PLA activity around Taiwan. Taiwan’s Ministry of National Defense (MND) reported 5 People’s Liberation Army (PLA) aircraft sorties, 6 navy ships and 9 “official ships” around Taiwan in the 24 hours to 6am on 19 October (local time), with 3 sorties crossing the median line (MND).
• Russian surveillance flight. Japan scrambled fighters on 17 October for a Russian IL-20 intelligence aircraft that flew over the Sea of Japan to off Kyoto Prefecture (JSO, 19 October, in Japanese).

What to watch next

• Landing drills by the Ground Self-Defense Force’s Amphibious Rapid Deployment Brigade at Kin Blue Beach and Camp Hansen, Okinawa, planned for 20 to 23 October (USNI News).
• An official US release on the American contribution, including whether Typhon is used.
• China’s response, both in statements and in naval and coast guard activity near the southwestern islands.
• The Joint Staff’s end-of-exercise summary after 29 October. It published one on Keen Sword 23’s results in 2022.

Sources

1. Japan Joint Staff Office: Japan-US joint exercise Keen Sword 27 (in Japanese), 29 September 2026
2. Japan Joint Staff Office: Japan-US joint exercise Keen Sword 25 (in Japanese), 26 September 2024
3. US Navy: USS Theodore Roosevelt arrives in Yokosuka, 16 October 2026
4. Japan Joint Staff Office: Movements of Chinese navy vessels (Liaoning), 14 October 2026
5. Japan Joint Staff Office: Movements of Chinese navy vessels (Liaoning), 15 October 2026
6. Japan Joint Staff Office: Movements of Russian military aircraft (IL-20), 19 October 2026
7. Taiwan Ministry of National Defense: PLA activities in the waters and airspace around Taiwan, 19 October 2026
8. USNI News: U.S., Japanese forces to rehearse defense of Japan’s southwest islands, 6 October 2026
9. Defense News: US Marine Corps anti-ship weaponry to see exercise action on remote Japan island near Taiwan, 5 October 2026
10. The Japan Times: Joint Japan-U.S. military drill set to break new ground, 18 October 2026
11. Yomiuri Shimbun: Long-range Type 25 missile joins Japan-US exercise for the first time (in Japanese), 19 October 2026
12. Kyodo News via Okinawa Times: Japan-US exercise with 50,000 personnel begins (in Japanese), 19 October 2026