Operation ‘High Mast’ was an eight-month long global deployment of the British Carrier Strike Group 2025 (CSG25) led by the aircraft carrier HMS Prince of Wales to the Indo-Pacific and Mediterranean. Beginning in April 2025, it formally came to an end in mid-December with the return of the carrier strike group to the UK.[i] Operation High Mast constitutes the Royal Navy’s largest maritime deployment and follows a similar deployment by HMS Queen Elizabeth in 2021-22 (which took place in the context of the Covid-19 pandemic). Alongside HMS Prince of Wales, it includes a type-45 destroyer HMS Dauntless, a type-23 frigate HMS Richmond and a raft of Royal Fleet Auxiliary support vessels.
It also includes several European and NATO partners, including the Norwegian frigate MnoMS Roald Amundsen, the Spanish frigate ESPS Méndez Núñez and the Canadian frigate HMCS Ville de Québec. Other allied ships, such as the Italian frigate ITS Luigi Rizzo, have also joined on a short-term basis. Sweden has also contributed staff officers who will serve on a rotational basis. The carrier group conducted training missions and exercises in the Pacific and Indian Oceans for five months before returning to the Mediterranean where it was placed under NATO command and took part in both Exercise Falcon Strike with Italy and NATO’s Exercise Neptune Strike. On 17 November 2025, it was announced that the CSG25 has reached ‘full operating capacity’, thus marking the first time NATO has had a European carrier strike group under its command with advanced 5th generation F-35Bs jets.[ii]
Operation High Mast is interesting for at least three reasons: (1) what it indicates about the UK’s post-Brexit foreign, security and defence policy; (2) what it demonstrates in terms of autonomous European power and influence in a world of great power competition in the Trump age; and (3) what it signifies for the deepening linkages between Europe and the Indo-Pacific region. This analysis addresses these issues, focusing on the implications of the carrier strike group deployment for European security and deterrence.
In terms of post-Brexit British foreign and security policy, the deployment of a carrier strike group to the Indo-Pacific region and the Mediterranean underlines the UK’s global interests as an island nation and a maritime trading power. Whilst British security policy is now primarily focused on the Euro-Atlantic area, and although London has quietly dropped the post-Brexit rhetoric of ‘Global Britain’, the UK still seeks to play a global role and cultivate relations with partners and allies beyond Europe.[iii] As a permanent member of the UN Security Council, it has an obligation to safeguard ‘international peace and security’. As a maritime trading power with global economic interests, the UK favours a rules-based international order including freedom of navigation and security of maritime trading routes (particularly in terms of security of supply chains and access to markets and critical raw materials).
The primary purpose of Operation High Mast was to underline the UK’s interests in the Indo-Pacific, which are economic, political, diplomatic and strategic. Approximately 17% of UK trade is with the Indo-Pacific region. Britain’s primary security and defence partnerships in the region are with Australia and Japan; both are underpinned by major defence-industrial projects: AUKUS and GCAP (Global Combat Aircraft Programme, a trilateral partnership between the UK, Japan and Italy to develop a next generation fighter jet). The UK has deep historical and cultural ties with Australia and New Zealand through the Commonwealth and through the Five Eyes Anglosphere signals intelligence alliance, which also includes Canada and the United States. Australia, the UK and the United States also cooperate in the AUKUS security partnership designed to ‘promote a free and open Indo-Pacific that is secure and stable’.[iv] Reflecting its character as a culturally diverse and multi-ethnic country, the UK has close relations with India and Pakistan, both of which are Commonwealth nations. Finally, like many other European countries, the UK is increasingly aware of the deepening linkages between security in the Euro-Atlantic and Indo-Pacific regions. Russia and China’s ‘no limits partnership’ as well as North Korea’s escalating military involvement in Ukraine demonstrate the interdependence of the two regions in the current global context.
Operation High Mast has primarily served as a demonstration of the UK’s global interests and its global maritime reach. However, it was also significant as a manifestation of an autonomous European capability in an age of both intensifying great power competition and growing doubts about the commitment of the United States to European security and defence. As noted above, Norway – the UK’s closest ally in the Nordic region[v] – committed a frigate to the entirety of the deployment, and other contributions came from Spain, Canada and New Zealand – but not the US Navy. Operation Highmast will include cooperation with US strike groups in a major exercise with Japan in the Northern Philippine Sea, but the US Navy is not part of CSG25.[vi] Operation High Mast was thus a significant demonstration of the RN’s ability to operate globally with allies and partners – if needs be, independently of the US. This is potentially significant as the Trump administration steps back from European security and Europeans are left facing the threat from Russia primarily on their own.[vii] CSG25 has illustrated the UK’s ability to operate independently from the United States if necessary. This is important as the UK seeks to build cooperation in the Wider North with countries such as Norway, Sweden and Canada with a view to confronting Russia’s Northern Fleet in the GIUK (Greenland-Iceland-UK) gap and creating an ‘Atlantic Bastion’.[viii]
It is also worth noting that the deployment of Carrier Strike Group 25 to Indo-Pacific took place in the face of explicit opposition from the Trump administration. In May 2025, Elbridge Colby, the US undersecretary of defence attempted to dissuade British officials from sending CSG25 to the Indo-Pacific arguing that ‘We don’t want you there’.[ix] This reflects the Trump administration’s attempt to detach its Pacific strategy from its European strategy, and to encourage Europeans to limit their security horizons to their immediate neighbourhood. However, this ignores the numerous ways in which security and diplomacy in the Indo-Pacific and Euro-Atlantic regions have become increasingly intertwined. China and Russia have drawn ever closer together; North Korea has supported Russia’s war against Ukraine with troops and ammunition; and Europeans have extensive defence-industrial links with Japan, South Korea, Australia and New Zealand. As the Swedish government noted when it announced Sweden’s participation in Operation Highmast, ‘developments in the Indo-Pacific region are increasingly affecting security in the Euro-Atlantic region, which includes Sweden’, and as Defence Minister Pål Jonson stated; ‘It is in Sweden’s interests to enhance defence cooperation with partner countries in the Indo-Pacific region. This increases our activity and enables us to gather additional knowledge of the security dynamic in the area’.[x]
Operation Highmast showcased the UK’s commitment to global maritime security and its ability to operate with non-US allies and partners. It began with participation in Exercise Med Strike in the Ionian Sea before transiting the Suez Canal, entering the Red Sea and sailing east across the Indian Ocean. The carrier group conducted a high profile visit to Singapore (where the Royal Navy has a logistics base) and then participated in Australia’s premier multilateral defence exercise Talisman Sabre (13 July-4 August). CSG25 visited Japan and exercised with the Japanese navy, and then held joint exercises with the Indian Navy (Exercise Konkan[xi]), ending in a port visit to Mumbai.[xii] During this eight month deployment, individual vessels contributed to a range of additional operations and missions, including transiting the Taiwan Straights (despite the reported concerns of the British Foreign Office[xiii]) and enforcing UN sanctions on North Korea. CSG25 enjoyed particularly close and sustained operational support from Norway, Canada and Spain, but also included participation of warships and support vessels from Australia, France, Italy, Japan, New Zealand, Portugal and the US – a total of ten NATO allies and partners.
It therefore served a raft of political, diplomatic, economic and strategic purposes that are important in the context of the uncertainties surrounding contemporary US foreign and security policy. It reinforced the UK’s commitment to global maritime security and strengthened linkages between European and Indo-Pacific allies. It demonstrated the global reach of the Royal Navy operating in partnership with non-US NATO allies and contributed to cementing key partnerships with Japan, Australia and India.[xiv] In doing so, it shows the capability and resolve of a middle-sized European power to act autonomously from the United States, thereby demonstrating a form of European agency in a competitive and uncertain world and potentially making the UK and Europe more attractive partners for the USA.[xv] It also a clear indication of an autonomous European commitment to a secure rules-based maritime order.
As Europeans digest the implications of the new US National Security Strategy and the UK government seeks to draw closer to its European allies and partners, Operation High Mast highlights the potential of European nations to take on greater responsibility for their own collective security and defence. One of the key lessons of CSG25 for the UK has been the importance of deepening operational cooperation with its non-US allies and partners; as UK Defence Minister John Healey noted ‘Our strength comes from hard power and strong alliances’.[xvi] Having demonstrated its ability to project power globally, the Royal Navy – with its two Queen Elizabeth-class carriers – has now refocused on its key role as a frontline high-readiness asset for NATO deterrence and defence. The primary focus of British maritime strategic thinking is increasingly the North Atlantic, High North and Nordic-Baltic theatre of operations, where British naval capabilities have much to contribute but where cooperation with allies is vital.[xvii] Effective cooperation and interoperability amongst European allies and Canada will be of growing importance for the Euro-Atlantic region in coming years. Operation High Mast provides invaluable lessons and operational experience for the UK and its allies to draw upon as they seek to strength Europe’s collective security and deterrence.