What US-Japan military exercises can tell us about their plans for a Taiwan conflict
Prime Minister Sanae Takaichi’s recent remarks started a major row with Beijing and shone a fresh spotlight on Japan’s strategic thinking
It also follows a steady build-up of supplies and equipment in the region by Japan’s main ally, the United States, in the past three months.
Yonaguni is the westernmost island in the Ryukyu chain, which would be a key strategic location in the event of a conflict over Taiwan.
The Japanese military has already spent years planning operations based on this precise scenario and although specific details have never been officially disclosed, past joint US-Japan exercises can help shed some light on their likely operational plan.
Her comments triggered the ongoing diplomatic row with Beijing, which regards the remarks as interference in its internal affairs and has demanded she retract them.
However, reports that the Japanese and US military were drafting a joint operational plan for a crisis in the Taiwan Strait first emerged in 2021, with media reports saying this would include the establishment of temporary offensive bases in the Ryukyu chain.
In the past two years, the frequency and scale of joint training exercises between the US and Japan have expanded significantly, with a greater focus on specific scenarios.
The exercise highlighted a number of problems in areas such as operations and logistics. Although these were never officially acknowledged, subsequent exercises and changes to the command structure appear to have been designed to address these.
The Keen Edge 2024 scenario involved the People’s Liberation Army attacking Taiwan and launching missile strikes on two US bases in Japan, the naval base in Sasebo in Nagasaki and the Iwakuni airbase in Yamaguchi.
The exercise also had the premise that a small group of PLA forces had landed on Yonaguni.
Tokyo did not classify this as a “direct attack on Japan”, which would allow it to exercise its right to self-defence under the post-war pacifist constitution that sets strict limits on when its forces can be deployed.
But Tokyo decided it would qualify as a “survival-threatening situation”, in which the Japan Self-Defence Forces (SDF) were authorised to use force under their right to collective self-defence.
This is a concept under international law that allows other states to come to the aid of one that has been attacked.
Legislation introduced in 2014 allows it to interpret the constitution so that “an armed attack against a foreign country with which Japan has close ties” or which “threatens the very existence of Japan” would allow Tokyo to invoke this right to collective self-defence.
During the exercise, the US military asked Japan to attack a PLA amphibious assault fleet navigating the Taiwan Strait, using its fighter jets to launch anti-ship missiles.
There was an internal debate within the Japanese forces regarding targets. Some commanders argued the priority should be sinking aircraft carriers, but the decision was made to target transport ships instead.
To retake Yonaguni, the Japanese ground forces dispatched reinforcement units to assemble in Kyushu, the southwesternmost of Japan’s home islands, but a critical logistical bottleneck emerged.
Ground forces’ transport aircraft were supposed to carry the troops while air SDF fighter jets were to conduct combat sorties, but this led to conflicts over who got priority to use the runways at some airbases and exposed gaps in joint operational planning.
Sankei did not report whether a solution to the runway conflict was reached or what the outcome of the simulated battle was.
The operation also presupposed the existence of a joint operations command, although this was only officially established in March this year to ensure better coordination between the various wings of the Japanese SDF and serve as the contact point with the US Indo-Pacific Command.
In the same month, the Japanese forces created a new Maritime Transport Group across its services to enable more rapid and reliable logistics.
The construction of a new airbase on Mageshima Island has also been accelerated. Featuring a 2,000-metre (6,510 feet) runway, the facility is designed to support air traffic across the Ryukyu chain and will also host US Navy field carrier landing practice.
The Ryukyus, an arc of more than 150 islands stretching more than 1,000km between Kyushu and Taiwan, are at the heart of the ongoing military build-up.
Since Keen Edge 2024, there have been various follow-up exercises focused on the island chain that addressed more specific issues.
For instance, the Iron Fist 2024 and 2025 exercises between the US Marine Corps and Japan’s Amphibious Rapid Deployment Brigade focused on rehearsing amphibious warfare tactics to recapture remote islands.
The Japanese amphibious brigade was established in 2018 and is specifically tasked with retaking islands through rapid manoeuvres and amphibious operations, prompting frequent comparisons with a marine corps. It was expanded in 2024 with the addition of a third regiment.
The 2025 edition of Iron Fist was double the scale of the previous year’s exercise and involved 4,000 personnel from both sides.
A naval helicopter airlifted amphibious brigade troops from a transport ship to an “enemy” camp on “occupied” Okinoerabu Island to launch an attack, while Japanese and US amphibious landing ships carried additional forces to the beachhead, local media reported.
The Typhon system can launch SM-6 air-defence missiles and Tomahawk land-attack cruise missiles capable of hitting the Chinese mainland if launched from Iwakuni, where the system was based during the exercise.
One of the largest biennial joint exercises was Keen Sword 2025, which Ryukyu Asahi Broadcasting described as a probable rehearsal of the US-Japan joint operational plan for a Taiwan Strait conflict.
It involved roughly 45,000 personnel from both countries, along with personnel from Canada and Australia, and saw the US station Himars (High Mobility Artillery Rocket System) units on Ishigaki island, around 270km east of Taiwan.
Ryukyu Asahi Broadcasting reported that under the joint plan suggested by the exercise, more missiles and Himars were likely to be deployed to the island chain and the Philippines to build a blockade line to contain PLA naval movements.
The Japanese forces would be expected to focus on rear support, providing essential logistics such as ammunition and fuel.
Meanwhile, Japan has been building up its defences along the Ryukyu chain. According to the 2025 Japanese Defence White Paper, surface-to-ship and surface-to-air missiles have been deployed on Amami Island, along with an electronic warfare regiment.
Air SDF squadrons along with new naval anti-ship and electronic warfare units have been deployed on Okinawa, the chain’s main island where there is a heavy US military presence.
The US Marine Corps also established a specialised littoral combat regiment on the island in 2023.
Missile units have also been established on other islands, including Miyako and Ishigaki, along with a variety of other units.
The recent missile deployment on Yonaguni marks the latest phase in a steady build-up that includes aircraft control and warning, electronic warfare and coastal surveillance units.
Miyako, Ishigaki and Yonaguni all form part of the Sakishima Islands, where the Japanese government has been developing emergency evacuation plans.
A preliminary plan announced in March set out how 110,000 residents and 10,000 tourists could be airlifted to the Japanese mainland within six days in the event of a conflict.
Reports that the Japanese and US militaries were drafting joint operations plans for the Taiwan Strait first emerged in the Japanese media in 2021, which said the US Marines would establish temporary offensive bases along the Ryukyu chain in the early stages of a conflict.
In January 2022, the US-Japan Security Consultative Committee, comprising foreign and defence ministers from both sides, agreed to officially begin working on a formal joint operation plan.
In December that year, the Japanese government released three documents covering its defence build-up programme and national security and defence strategies, and formally stated its policy was to possess “counter strike capabilities” to attack enemy bases.
Beijing views Taiwan as part of China, to be reunited by force if necessary.
Japan and the US, in common with most countries, do not recognise Taiwan as an independent state, but they oppose any attempt to take the self-governed island by force and Washington is legally bound to provide arms to help it defend itself.