India's strategic posture in the Indo-Pacific is undergoing a transformative shift as concern grows in New Delhi over China's increasingly assertive maritime presence across the region and over the growing size of China's navy.
Japan's concerns around China's assertiveness are clear, as China's unilateral naval and air exercises are increasing in frequency and scope. Justice Mission 2025, Beijing's latest large-scale exercise around Taiwan, saw 130 PLA air sorties, 90 of which crossed the Taiwan Strait Center Line. Further east, the number of Chinese vessels recorded in the contiguous zone around the Japan-controlled Senkaku Islands reached a record high in 2025.
In January, the US's response was made explicit, with a new National Defense Strategy committing to expanded military capabilities in the Indo-Pacific with the goal of deterring China from dominating the region.
For Indo-Pacific democracies like India and Japan, however, the threat is more immediate. In response, both Tokyo and New Delhi are recognising that deeper security cooperation offers the most effective counterbalance.
Increasing cooperation between these two major military powers on opposing flanks of the Indo-Pacific would be a powerful step to create a counterweight to the possible future of China's increasing unilateralism.
India and Japan are already embedded within regional security frameworks. Both are members of the Quadrilateral Security Dialogue (Quad), an informal partnership with the US and Australia aimed at countering hostile interference and protecting maritime security. Yet it is under Japan's current administration that prospects for deeper cooperation have truly grown.
During the 18th Japan-Indian Foreign Minister's Strategic Dialogue in January, both nations reiterated their commitment to Japan's 'Free and Open Indo-Pacific' (FOIP) vision. FOIP seeks to deepen collective security cooperation with like-minded nations to uphold international law and deter coercive maritime practices.
As the region grapples with a worsening strategic environment, deeper India-Japan maritime cooperation under FOIP could serve as a powerful and increasingly necessary stabilising force.
For India, the strategic stakes are clear. Protecting shipping lanes and preserving freedom of navigation are national imperatives.
Approximately 95% of India's total trade transits the waterways of the Indian Ocean, including the bulk of its energy imports. Consistent and uninterrupted access to the sea has been the silent driving force behind India's economic rise over the past decade. Any erosion of India's ability to protect these routes would severely undermine its economic security.
In response, India has prioritised the expansion of its blue-water fleet, with plans to deploy more than 200 ships and submarines by 2035. India is also strengthening interdiction and surveillance capacity, including the induction of 16 Anti-Submarine Shallow Watercraft, and the commissioning of the INAS Ospreys, its second naval air squadron, in December 2025.
Yet New Delhi recognises that Indo-Pacific security cannot be upheld without regional partnerships. In 2015, at a similar time to Japan's pioneering of FOIP, Prime Minister Narendra Modi detailed the Security and Growth for All in the Region (SAGAR) doctrine.
SAGAR, like FOIP, advocates for collective security efforts across the Indo-Pacific and rests on the principle that responsibility for maintaining stability must be shared among capable and like-minded regional partners.
The doctrinal overlap is clear. India and Japan face similar strategic pressures and share a belief that a rules-based maritime order serves both their security and economic interests.
Like India, Japan is also stepping up a program of force modernisation. Defence Minister ShinjirΕ Koizumi has warned that the region is facing its most severe security environment since the Second World War, and the government has responded. Japan's defence budget is expected to exceed 5.2 trillion rupees for the first time, while a comprehensive review of its three core strategic documents is set to be completed by the end of 2026.
Tokyo is looking to expand its defence capabilities, investing in unmanned reconnaissance systems and stand-off missile capabilities to expand its long-range strike capabilities.
This strategic convergence is also extending beyond the military domain. During the same foreign minister's dialogue, India and Japan announced the launch of the Private-Sector Dialogue on Economic Security, aimed at strengthening the resilience of supply chains across five strategic sectors, including critical minerals and semiconductors.
While not a defence agreement in itself, the announcement reinforces the same logic β reducing vulnerability and building resilience against external pressures. India and Japan are cooperating, reducing supply chain risks as part of their drive to deepen ties with like-minded countries.
As the geopolitical clouds darken and as China's growing military capabilities contribute to eroding the Indo-Pacific's status quo, the linkage of two capable military powers on opposing flanks of the Indo-Pacific takes on added significance.
India and Japan share a common interest in upholding the primacy of international law. As two maritime powers modernising in parallel and coordinating more closely, their partnership is well placed to serve as the stabilising force in an increasingly contested Indo-Pacific theatre.
[Disclaimer: This is an authored article by Samir Puri, visiting lecturer in war studies at King's College London and author of Westlessness: The Great Global Rebalancing.]
