Joint Japan UK drills prepare forces for rapid island defense and contested littoral operations.

Japan’s Ground Self-Defense Force and the British Army ran Exercise Vigilant Isles 25 in Hokkaido from 5 to 20 November, combining joint airborne drops with Japan’s Amphibious Rapid Deployment Brigade for the first time. The drills deepened UK-Japan integration on island defense and layered coastal denial at a moment of rising tension around the East China Sea and Taiwan.

Japan’s Ground Self Defense Force confirmed that Exercise Vigilant Isles 25 wrapped up in Hokkaido after two weeks of intensive field training with the British Army, including a landmark joint airborne drop from Japan Air Self Defense Force C-130H transports and the first involvement of the Amphibious Rapid Deployment Brigade. British paratroopers from 2 PARA jumped using Japanese static line parachute systems, then linked up on the ground with Japan’s 1st Airborne Brigade and ARDB AAV 7 units in scenarios focused on defending and recapturing remote islands, according to Japanese defense officials' releases.
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For Japan, the exercise mainly highlighted the integration of airborne units of the Japan Ground Self-Defense Force (JGSDF) with the Amphibious Rapid Deployment Brigade (ARDB), a marines-type formation created in 2018 to defend remote islands and conduct littoral operations (Picture source: Japan GSDF)

The core of Vigilant Isles 25 rested on combined airborne activity at Enami, where British paratroopers trained with Japan’s 1st Airborne Brigade. This formation of around two thousand personnel, specializing in parachute and heliborne insertions for rapid reaction and island defense missions, formed the Japanese side’s main maneuver element. Soldiers from the 2nd Battalion, The Parachute Regiment (2 PARA) jumped from JASDF C-130H aircraft in static-line mode using Japanese parachutes. This change from their usual procedures required British personnel to adapt to a different equipment standard and to other methods for checks in the aircraft, exit, and regrouping on the ground. Live-fire sequences included observation of a Japanese ground-based coastal missile system, giving British observers a detailed view of the detection-to-engagement sequence in a cold, snow-covered environment.

For Japan, the exercise mainly highlighted the integration of airborne units of the Japan Ground Self-Defense Force (JGSDF) with the Amphibious Rapid Deployment Brigade (ARDB), a marines-type formation created in 2018 to defend remote islands and conduct littoral operations. The brigade deployed its AAV-7 amphibious vehicles, which can leave a landing ship, travel several kilometers at sea at roughly 13 km/h, and deliver an infantry section directly onto a contested beach under light armor protection. This profile remained central to any scenario involving the recapture of occupied islands. In parallel, Japan continued to build up the ARDB’s air-mobile component. V-22 Osprey aircraft, with a planned fleet of seventeen platforms, were being gradually concentrated between Camp Saga and Camp Ainoura to provide a radius of action of several hundred kilometers toward the southwestern archipelagos. Even though these V-22s were not the visible focus of Vigilant Isles 25, the exercise prepared exactly the types of fire and maneuver combinations that such platforms are expected to support.

On the British side, Vigilant Isles 25 fitted into the mission set of the 16 Air Assault Brigade Combat Team, the British Army’s rapid reaction formation. Previous iterations had already deployed more than one hundred British soldiers to Japan for island defense training alongside JGSDF units. In 2025, the format moved up a level, shifting from parallel training to genuine airborne integration, with a combined drop, cross-use of national parachute systems, and direct exposure to Japanese unmanned systems and live coastal missile firings. For 2 PARA, which usually operates from Royal Air Force (RAF) platforms, jumping from JASDF-operated C-130H aircraft following Japanese procedures added a useful layer of complexity that can be applied to any expeditionary operation mounted from allied bases.

The exercise refined staff procedures that are less visible but decisive. Shared planning formats, coordinated fire support in a multinational environment, and practical use of the Reciprocal Access Agreement between the United Kingdom and Japan facilitated the movement of troops, equipment, and ammunition on Japanese territory. Repeated exposure to national live-fire regulations, medical evacuation chains, and safety procedures reduced the time needed to assemble a credible combined force in a crisis. The presence of British observers during Japanese missile firings, along with the involvement of Japanese officers in British planning cells, illustrated a gradual convergence around the concept of layered coastal defense.

Beyond its immediate military value, Vigilant Isles 25 also had an impact on political signaling in the Indo-Pacific. The joint airborne drop on Japanese territory, the visible presence of British paratroopers in Hokkaido, and the integration of Japanese amphibious forces all took place in the framework of the Hiroshima Accord and a defense agenda that is becoming denser between London and Tokyo. Combined with the Reciprocal Access Agreement, the exercise helped anchor the presence of European land forces within Japan’s island defense planning at a time of heightened tensions in the East China Sea and around Taiwan. For regional actors, the message that emerged remained clear. The evolution of Japan’s amphibious and airborne postures no longer belonged solely to a national framework but was part of a network of partnerships that now links Europe directly to the security of the Western Pacific.