In August 2020, Japan’s then Defence Minister, Kōno Tarō – now a popular Vaccines Minister and frontrunner to succeed Suga Yoshihide as Prime Minister – made clear his country’s ambition to join the world’s most powerful, durable, and consequential intelligence alliance in the history of international relations, the so-called ‘Five Eyes’ comprising the United States, the United Kingdom, Canada, Australia, and New Zealand. ‘Japan’, he stated, ‘can get closer [to the alliance] even to the extent of it being called the “Six Eyes”.’ But how realistic is this? What considerations matter? And do all parties comprehend the same idea and reality of Five Eyes?

Strategic interests and threat perceptions

Japan’s timing for a push for membership may seem propitious in the current strategic environment. Tokyo and Five Eyes capitals hold increasingly – though not totally, in Wellington’s case – aligned threat perceptions regarding a key target for intelligence collection and cybersecurity. China’s regional hegemonic ambitions and coercive behaviour has prompted growing concern and strategic reconsiderations not only from Washington to Canberra – exemplified by US President Joe Biden’s lobbying for aligned security policy towards China at the G7 and NATO summits in June 2021 and the new Australian-United Kingdom-United States (AUKUS) defence technologies partnership – but also in capitals across the Indo-Pacific.

In Tokyo, Japanese defence policy towards its largest trading partner has become increasingly assertive since former Prime Minister Abe Shinzō’s election in 2012. Japan’s pursuit of enhanced bilateral and multilateral security guarantees aligns with Biden’s stated deeper commitment to America’s treaty partner, London’s post-Brexit Indo-Pacific ‘tilt’ espoused in the 2021 ‘Integrated Review’, and Canberra’s 2020 Defence Strategic Update. This is manifesting through a series of overlapping ‘minilateral’ forums like the Quadrilateral Security Dialogue, or ‘Quad’, whose American, Australian, Japanese, and Indian leaders meet in Washington this week.

Extending intelligence cooperation is a natural and necessary adjunct to this latticework of relationships. But this does not make the Five Eyes alliance the best-suited avenue to achieve this. Prominent champions of Japanese membership in American, British, and Australian legislatures and Japan’s media, who alongside ministers increasingly use ‘Five Eyes’ as diplomatic shorthand for member government cooperation on a range of geostrategic issues, misunderstand the reality of the alliance.

The reality of Five Eyes

Unlike other sanitised and ritualistic multilateral intelligence and security forums, Five Eyes is a point of collective strength for its members – the signals intelligence (SIGINT) and cyber services of the five states – defined by seventy-five years of institutionalisation, interoperability, and trust. Originating in the Second World War, the globally and functionally wide-ranging 1946 UKUSA Agreement and updated agreements that welcomed Canada, Australia, and New Zealand between 1948 and 1956 have set a default baseline for sharing ‘continuously, currently and without request’ unprocessed and assessed SIGINT and accompanying the cryptanalytical and encryption methods.

Adapting to the mutual threat environments and technological changes of the Cold War and post-9/11 ‘Global War on Terror’, the alliance represents the process and product of an ever-evolving organic harmonization of member service capabilities, systems, and organisational cultures – including near full-access liaison officers (so-called ‘integrees’) – aided by synergies in the like-minded liberal, Anglophone political cultures they form a part of. That in the wake of 9/11, then National Security Agency Director Michael Hayden entrusted the management of the US SIGINT system to Britain’s Government Communications Headquarters in the event of a catastrophic event at Fort Meade, NSA’s headquarters, exemplifies Five Eyes’ remarkable interoperability, intimacy, and inter-personal trust. As Hayden explained regarding Germany in 2015, this makes access near impossible for prospective third-parties.

Japan is a liberal democracy with a Directorate for Signals Intelligence that now shares some characteristics in common with the Five Eyes services and eleven new listening posts built in the last decade that enhance collection capabilities on prominent Five Eyes targets China, North Korea, and the Russian Far East. Its established status as a technological innovator in fields such as satellites, artificial intelligence, and quantum is attractive. Abe-era security sector reforms have addressed a long history of inter-agency bureaucratic competition and given allies more confidence to share their secrets in new bilateral defence mechanisms by passing Japan’s first post-war state secrecy law. But these capabilities are likely insufficient to meet Five Eyes’ requirements and outweigh fundamental differences in structures, organisational cultures, language for exchange, and legal authorities governing SIGINT that remain major barriers to full-fledged membership.

Admission would also require willingness to reveal members’ collection requirements, capabilities, and weaknesses to Japan, highly sensitive strategic concerns. Even more momentously, admission would mean a no-spy agreement, a unique core tenet of Five Eyes that does not even cover other NATO allies. Japan itself would need to be more comfortable with an unheralded degree of partner transparency than its intelligence community has historically been comfortable with in multilateral forums. Notably, unlike fellow Quad member India, in 2007 Japan reportedly turned down the opportunity to advance institutional synergies and trust through joining ‘SIGINT Seniors Pacific’, part of a semi-formalised inner and outer penumbra of separate discretionary intelligence exchange and technical support systems for more trusted third-parties of Five Eyes.

The implications of Japan or additional third-parties deepening their diplomatic and defence cooperation with Five Eyes member governments concerning China, therefore, are very different to being granted full membership of a global SIGINT network that is not a single-issue alliance and has developed organically and uniquely without a new member in sixty-five years. Interested parties should avoid conflating the two. In this inherently conservative field, gaining a more trusted third-party ‘Five Eyes-plus’ status akin to, or ahead of, other European and Indo-Pacific powers, with compartmentalised but free-flowing SIGINT on China and North Korea, may be a more realistic aim for Tokyo and, indeed, given the sensitivities of ‘joining Five Eyes’, a more satisfactory end-state for all parties.

Thomas J. Maguire is an Assistant Professor of Intelligence and Security at Leiden University and a Visiting Fellow at the Department of War Studies, King’s College London, and David V. Gioe is an Associate Professor at the Army Cyber Institute, West Point, and a British Academy Visiting Professor at the Department of War Studies, King’s College London. This analysis does not reflect any official U.S. government position.