The Japan-UK defence partnership focuses on cybersecurity, GCAP and joint military exercises across the Indo-Pacific region.

 

The defence partnership between Japan and the UK has evolved into one of the most consequential strategic alliances in the Indo-Pacific. 

Both nations view each other as one of their closest security partners in Asia and Europe respectively. Strategic dialogues at ministerial and vice-ministerial levels ensure momentum, with discussions spanning cybersecurity and emerging technologies. The countries have also reinforced diplomatic ties by expanding defence staff within their embassies and coordinating closely on economic security.

The UK is sending a large contingent to DSEI Japan, comprising 344 attendees, including 158 exhibitors, 58 VIPs, and 52 government officials, demonstrating their intentions for significant institutional engagement.

What are the UK's defence priorities?

The UK's defence budget for 2025-26 is projected to reach GBP67.7 billion (2.5% of GDP), up from GBP64.4 billion for 2024-25. The funding aims to modernise its armed forces, replenish munitions stockpiles and acquire advanced defence technologies like drones and autonomous systems. 

Defending Britain policy paper, published in April 2024 emphasises strengthening alliances such as AUKUS and NATO and prioritising partnerships to enhance global security. It aligns with the Integrated Review Refresh 2023, positioning the UK to address emerging threats and maintain strategic resilience.

The UK’s Strategic Defence Review 2024-2025, due to be published in Spring 2025, aims to redefine roles and capabilities in response to hybrid warfare threats and a volatile global landscape. Key themes are likely to include reinforcing NATO commitments, enhancing national security and maintaining support for Ukraine. The parallel Defence Industrial Strategy is expected to prioritise partnerships with SMEs and aims to streamline procurement  to encourage innovation and economic growth.

The Hiroshima Accord operationalises the Japan-UK partnership

Central to the Japan-UK collaboration is the Hiroshima Accord, which provides a comprehensive roadmap for deepening interoperability, joint exercises and advanced defence technology cooperation. 

Signed in 2023, the accord prioritises military interoperability through the Japan-UK Reciprocal Access Agreement (RAA), which was signed earlier that year. The RAA was first applied in November 2023 during Exercise Vigilant Isles, a bilateral island defence drill between the Japanese and UK armies. Other joint initiatives include:

• Global Combat Air Programme (GCAP): A trilateral project with Italy to develop a sixth-generation fighter jet by 2035, integrating Japan-UK defence industries and securing high-skilled jobs through shared R&D and supply chain integration.

• Operational collaboration: Deployment of the UK’s carrier strike group to the Indo-Pacific in 2025 and expanded amphibious/airborne unit exercises to counter regional instability.

• AUKUS Pillar 2 collaboration: Consultation with Japan for potential involvement in advanced military technologies under AUKUS Pillar 2, including quantum computing, AI, hypersonic missile defence and undersea warfare systems.

Cybersecurity collaboration

The Hiroshima Accord is notable for its emphasis on emerging technology domains through the Japan-UK cyber and semiconductors partnerships, which reflect the countries' recognition of the importance of digital resilience and supply chain security. 

These partnerships prioritise defence-focused collaboration through shared threat intelligence frameworks, joint capacity-building programmes and harmonised responses to state-sponsored cyber threats. 

A cyber threat intelligence-sharing alliance, enacted under the accord, enables the real-time exchange of data on advanced persistent threats targeting critical national infrastructure to align defensive strategies against hybrid warfare tactics. The partnership strengthens operational resilience through co-developed AI tools for anomaly detection in military networks and joint res

earch into post-quantum cryptography to safeguard classified communications. 

Private sector integration is facilitated via the UK-Japan Tech Forum, where defence contractors and cybersecurity firms collaborate on penetration testing standards and supply chain security protocols.

By embedding cybersecurity into bilateral defence policy, the partnership addresses vulnerabilities in interconnected command systems while deterring adversarial cyber campaigns across the Indo-Pacific and Europe.

The JAGUAR universal radio frequency sensor project

The Japan and Great Britain Universal Advanced RF (radio-frequency) sensor system (JAGUAR) is a five-year UK-Japan defence collaboration launched in April 2022. 

It aims to develop advanced multi-domain threat detection technology by combining expertise from Leonardo UK and Japanese industry partners to create a sensor capable of identifying air, land, and sea threats while countering adversarial surveillance. Supported by GBP2 billion in UK Combat Air Strategy funding, the initiative involves building dual demonstrators (one per country) to refine capabilities like target geolocation and electromagnetic spectrum dominance, aligning with sixth-generation fighter jet programmes such as GCAP and Japan’s F-X. 

 

DSEI Japan

DSEI Japan 2025 is the forum where international companies can understand Japan's evolving defence posture, build relationships with key stakeholders and develop informed strategies for supporting Japan's defence modernisation efforts. With a large percentage of attendees from the Indo-Pacific region and strong representation from Japanese small and medium enterprises,  DSEI Japan 2025 provides an ideal environment for exploring potential industrial partnerships and understanding the local defence industrial base.

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