Exercise Vigilant Isles 2025 has been completed, having been conducted from January 15, 2025, to January 26, 2025, in Japan. This exercise added one more brick to the growing defense cooperation and partnership between the UK and Japan. Exercise Vigilant Isles 2025 involved the UK’s 16 Air Assault Brigade, which deployed around 100 British soldiers. These soldiers took part in the exercise along with their counterparts from the 12th Brigade and 1st Airborne Brigade of the Japan Ground Self-Defense Force (JGSDF).

The soldiers displayed live exercises, joint planning, and combat simulation drills akin to real-world battle scenarios, with a focus on airborne battle plans and quick reaction deployments. Exercise Vigilant Isles 2025 was conducted on the island of Kyushu, Japan.

At the beginning of the exercise, UK Defense Secretary John Healy and Japan’s Defense Minister Gen Nakatani met in London to discuss the defense partnership between the UK and Japan, focusing on developments in the GCAP (Global Combat Air Program).

With increasing instability across the world, it is more important than ever that we strengthen cooperation with our international partners like Japan. Today, Minister Nakatani and I have highlighted the positive progress being made on our important next-generation fighter jet program, to strengthen our security cooperation. There are many miles between our two nations, but the UK and Japan stand closer together than ever in support of peace and security across the globe.

Defense Secretary, John Healey, UK

Later in 2025, the UK Navy will dispatch its Carrier Strike Group to Japan as part of the 2025 Indo-Pacific deployment. This Carrier Strike Group will include HMS Prince of Wales and the onboarded aircraft, accompanied by escort vessels. They will work in cooperation with Japan’s Self-Defense Force to uphold peace and stability in the Indo-Pacific waters.

“The training we have done with the Japanese has developed our understanding of each other’s capabilities but will also benefit our soldiers whatever their next challenge is. Training in such an unfamiliar and demanding environment and learning from how the Japanese operate in these conditions will only improve our skills.”

Major Iain Thompson, Commanding Officer, British Paratroopers

What is Exercise Vigilant Isles?

Exercise Vigilant Isles is a bilateral military exercise conducted between the United Kingdom and Japan to grow defense cooperation, inter-operability, and strategic partnership between their military forces. It involves troops from the UK’s 16 Air Assault Brigade and the Japan Ground Self-Defense Force (JGSDF), particularly its airborne and quick reaction units. The exercise typically includes live battle drills, joint planning, and battle training that simulate real-world war situations. Exercise Vigilant Isles is one of the components of the broader security collaboration between the UK and Japan, which showcase their joint commitment to ensure stability in the Indo-Pacific region. As of 2025, UK & Japan have completed 3 such military exercises.

What is Global Combat Air Program (GCAP)?

The Global Combat Air Program (GCAP) is a joint initiative between the United Kingdom, Japan, and Italy to co-develop a next-generation advanced aircraft designed to counter modern aviation threats.

The UK, Japan, and Italy have already signed the GCAP Treaty, leading to the establishment of the GCAP Headquarters in Reading, UK. The GCAP International Government Organization (GIGO) is currently led by its CEO, Mr. Oka Masami from Japan.

BAE Systems (UK), Leonardo (Italy), and Japan Aircraft Industrial Enhancement Co. Ltd. (JAIEC) are collaborating to develop this advanced fighter aircraft, which will be utilized by all three nations. This venture also includes a robust revenue generation plan aimed at creating employment opportunities for relevant personnel across the UK, Japan, and Italy.

The Importance of UK-Japan Military Cooperation

From a geopolitical perspective, UK-Japan military cooperation is extremely important and plays a crucial role in Indo-Pacific security, as the region’s waters host major global trade routes.

Additionally, the growing North Korean missile arsenal and an unpredictable China, which is planning to invade Taiwan and making territorial claims on various islands in the East and South China Seas, push a serious threat to Japan. UK-Japan military cooperation and strategic ties help Japan check these security challenges and maintain regional stability.

Reciprocal Access Agreement (RAA)-2023

The RAA signed between the UK and Japan allows for the deployment of forces in each other’s countries and facilitates larger-scale, more complex military exercises. This agreement underscores the commitment of both nations to rapidly accelerate defense and security cooperation. The Reciprocal Access Agreement (RAA) between the United Kingdom and Japan was signed on January 11, 2023 in London by UK Prime Minister Rishi Sunak and Japanese Prime Minister Fumio Kishida.

The Hiroshima Accord-2023:

The United Kingdom & Japan also signed Hiroshima Accord on 18^th May 2023 between British PM Rishi Sunak and Japanese PM Fumio Kishida to enhance the inter-operability, cross-domain defense & security cooperation, strategic partnership, semi-conductor trades & research.

The Hiroshima Accord encompasses fresh agreements in defense, trade, and investment, as well as collaboration in science and technology. Additionally, it outlines joint efforts to address global challenges, including climate change.

UK-Japan military cooperation, as demonstrated through Exercise Vigilant Isles, the Reciprocal Access Agreement (RAA), and the Hiroshima Accord, is set to have a significant impact on the security dynamics of the Indo-Pacific waters.

This strong collaboration greatly enhances intelligence sharing and interoperability, enabling both nations to effectively counter China’s ambitions in the East and South China Seas and address the growing North Korean missile threat.

As the United Kingdom increases its military presence in the Indo-Pacific through such exercises, its cooperation with Japan, freedom of navigation operations (FONOPs) and the security of global trade routes remain top priorities. These objectives will be secured well through joint military exercises in the Indo-Pacific region, like Exercise Vigilant Isles 2025, ensuring stability and deterrence in the zone. By conducting joint military exercises, Japan and the UK will help reinforce international laws governing the Indo-Pacific, ensuring that critical trade routes remain open and free from coercion.