With Japanese Prime Minister Fumio Kishida visiting Washington this week, rumours have circulated that Japan might soon join the AUKUS security pact between Australia, the United States and the United Kingdom.

Australian Prime Minister Anthony Albanese has downplayed the suggestion, indicating this is not something that will happen soon. He added any cooperation would, for now, be on a project-by-project basis.

What role could Japan possibly play in the alliance? And what are the potential complications?

Japan has grown increasingly uncomfortable at China’s assertiveness in the Indo-Pacific region, including its “wolf warrior” diplomacy, frequent cyber attacks and harassment of other countries’ ships and aircraft. China also has an ongoing dispute with Japan over islands in the East China Sea.

It’s not surprising, then, that Japan has doubled down on its alliance with the US and security ties with other like-minded nations. It was an early supporter of AUKUS, viewing the alliance as a positive step for regional security that would counterbalance China’s heavy-handed influence.

For some time now, Japan was talked about as a potential fourth partner in the agreement. While the US, UK and Australia have all said they are interested in working with Japan, however, a formal invitation to become a so-called “Pillar I” partner is not likely anytime soon.

The Pillar I level of the partnership involves the US transferring nuclear submarine propulsion technology to Australia. In the meantime, the US will operate a rotational submarine force in Western Australia, until Australia is supplied with refurbished, second-hand US Navy Virgina Class submarines, expected in the........

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