The Indo-Pacific Submarine Race: Power Politics Beneath the Waves

Beneath the calm waters of the Indo-Pacific, an invisible arms race is getting momentum. Submarines, often called the silent service of modern navies, have re-emerged as decisive instruments of strategy in the Indo-Pacific. Their value lies not just in stealth and deterrence but in their ability to operate freely across some of the world’s most contested waters. From the Indian Ocean to the South China Sea, nations are investing heavily in undersea deterrence to secure both their sovereignty and geopolitical leverage.

The undersea domain offers what surface warfare cannot, stealth, second-strike capability, and deterrence through uncertainty. In the Indo Pacific region, where the security architecture is fragmented, control beneath the waves increasingly dictates influence above them. 

The Indo-Pacific as the Epicentre of Submarine Competition

The Indo-Pacific today represents both the world’s busiest trade corridor and its most contested strategic zone. China’s People’s Liberation Army Navy (PLAN) has expanded rapidly, operating roughly seventy submarines, a mix of conventional and nuclear-powered boats some of which now conduct regular patrols into the Indian Ocean. Its expanding base in Hainan and forays into Gwadar and Djibouti highlight a sustained intent to project power far from its coastline. 

In response, regional actors are recalibrating. Japan is modernising its Soryu-class submarines with lithium-ion batteries to improve underwater endurance. Australia, through the AUKUS partnership, is moving toward acquiring its first nuclear-powered fleet. South Korea’s KSS-III programme also points to ambitions that go well beyond coastal defence. Together, these developments reflect how the underwater arena is becoming a key front in the Indo-Pacific’s strategic competition where advances in technology are directly shaping deterrence and regional security. 

The AUKUS Effect: Nuclear Ambition and Strategic Signalling 

The AUKUS agreement between Australia, the UK, and the US, announced in 2021, changed how Australia plans its future naval strategy. Now, it allows the country to build nuclear-powered submarines for the first time. Unlike its existing diesel fleet, these subs can travel longer distances and stay underwater for extended periods. This means Australian patrols could reach deeper into the South China Sea or the Indian Ocean without needing to surface often.

While hailed by the U.S. as a pillar of ‘collective deterrence’, AUKUS has provoked unease among the ASEAN members wary of nuclear escalation and China’s sharp response. Beijing’s criticism of ‘Cold War blocs’ conceals a deeper concern that nuclear-powered submarines could compromise its bastion strategy in the South China Sea. 

For India, AUKUS represents both an opportunity and a warning. It reinforces the Indo-Pacific as a multipolar maritime space, yet also underscores the widening technological gap in the under sea warfare.

Project 75(I) and India’s Efforts to Strengthen Undersea Capabilities

India’s submarine program, centered on Project 75 and the upcoming Project 75(I), aims to close the country’s undersea capability gap. The introduction of the Kalvari-class (Scorpene) submarines not only added new assets to the fleet but also helped revive India’s domestic shipbuilding industry. However, delays in air-independent propulsion (AIP) systems and slow decision making have constrained India’s expansion.

The government’s approval for building six new AIP-equipped submarines under Project 75(I), alongside plans for nuclear-powered attack submarines (SSNs), signals a renewed focus on strategic autonomy. If executed effectively, this will complement India’s Arihant-class SSBNs, creating a credible sea-based deterrent as part of its nuclear triad.

Beyond hardware, India’s undersea partnerships under the Quad with the U.S., Japan, and Australia are enhancing undersea domain awareness (UDA). Shared surveillance, seabed mapping, and data fusion could offer India a technological edge, even as it continues to rely on Russia for legacy maintenance and design inputs. 

China’s Expanding Undersea Footprint

China has been steadily extending its naval presence through bases in Djibouti, Cambodia, and Pakistan. Often described as a modern “string of pearls,” this network allows Beijing to support its submarines and other naval assets far from home waters. Beyond logistics, it gives China the ability to maintain a continuous presence in strategic maritime zones. 

The PLAN (People’s Liberation Army Navy) has also been developing advanced submarines, including the Type 094 and Type 095 nuclear-powered boats. At the same time, China is experimenting with unmanned underwater vehicles and seabed sensor networks to monitor foreign movements in the South China Sea. 

For smaller Indo-Pacific nations, these developments are challenging. They must navigate questions of alignment, sovereignty, and maritime law, especially as more nuclear-capable submarines operate in regional waters. These dynamics are reshaping how countries approach naval diplomacy, deterrence, and regional security.

The Legal and Governance Vacuum Beneath the Waves 

While maritime law under UNCLOS (1982) governs surface and seabed activity, it remains largely silent on military uses of the underwater domain. Nuclear submarine patrols, intelligence operations and deep sea sensor networks exist in legal grey zones. The proliferation of AUKUS-style transfers further strains the non-proliferation regime, an enriched uranium for propulsion skirts IAEA safeguards. 

ASEAN’s Treaty of Southeast Asia Nuclear Weapon-Free Zone (SEANWFZ) does not explicitly cover nuclear-powered submarines, leaving regional states vulnerable to interpretive loopholes. As nations push the boundaries of what is legal under the sea, the need for a new ‘code of conduct’ on undersea military activity becomes urgent.

The Emerging Balance: From Sea Denial to Sea Control

The Indo-Pacific submarine race reflects a transition from coastal defence to active sea control.For China, submarines serve to deter intervention and secure maritime dominance. For India and Japan they offer an asymmetric counterweight to larger navies. For Australia and the US, they ensure a credible forward presence.

Yet, the more submarines patrol these contested waters, the greater the risk of accidental escalation. Encounters beneath the waves lack communication channels or confidence building mechanisms. A collision between nuclear submarines or even a misinterpreted acoustic signal could spark a crisis no one sees coming.

The Future Lies Below

As global attention shifts to hypersonics and AI, the Indo pacific real contest continues silently underwater. Submarines are no longer mere tactical assets, they are instruments of diplomacy, deterrence and national identity. For India, mastering this domain is not just a technological necessity but a geopolitical imperative that will determine how credible it can shape the future Indo Pacific order.

In the end, power in the 21st century may not rest with those who command the skies, but with those who command the depths.