India is on the verge of significantly strengthening its nuclear triad with the commissioning of its third indigenously developed nuclear-powered submarine, INS Aridhaman.

This milestone substantially enhances India’s second-strike capability, providing strategic reassurance for those tasked with protecting the nation’s maritime boundaries and interests.

Despite prolonged deliberations over adding six new diesel-electric submarines, the ageing conventional Indian fleet urgently needs renewal. Half of its diesel-electric submarines — including six Kilo-class vessels nearing thirty years of service and four German HDW submarines older than three decades — raise serious operational concerns.

These submarines constitute almost half of India’s total diesel-electric fleet of eighteen. Given the evolving maritime threats, the Indian Navy must modernise its underwater assets to maintain credible deterrence and operational reach.

India’s nuclear submarine program has steadily progressed since the induction of INS Arihant in 2016 and INS Arighaat in 2024. These vessels are the core of India's sea-based nuclear deterrence, representing generations of indigenous design and technology.

Earlier Indian experience with Russian nuclear submarines — the leased Chakra-1 in the late 1980s and Chakra-2 in the early 2010s — provided vital operational knowledge that inspired domestic efforts towards independent nuclear propulsion development.

Russian assistance has been pivotal, particularly in the sensitive area of nuclear propulsion technology. Despite international technology denial regimes led by the United States and Western nations, Indian strategic planners pursued indigenous mini-reactors for nuclear submarines, supported by Russian engineers’ expertise.

This collaboration underscores the special strategic partnership between India and Russia in defence technology transfer and development.

Maritime security challenges in the Indian Ocean and beyond demand platforms capable of extended deployment without reliance on external support. Nuclear-powered submarines offer unmatched endurance — able to operate underwater for months, in stark contrast to the limits of diesel-electric and Air Independent Propulsion (AIP) submarines.

Although AIP technology extends submerged endurance up to roughly two weeks, crew endurance remains a limiting factor, rendering AIP submarines inferior for sustained blue-water operations. Notably, India currently lacks AIP-equipped submarines, while Pakistan is upgrading its fleet with Chinese Yuan-class diesel-electric submarines equipped with AIP, gaining a regional undersea advantage.

China’s expanding naval footprint in the region further complicates strategic calculations. Beyond supporting Pakistan’s submarine programme, China has delivered second-hand submarines to Bangladesh and is building a significant submarine base at Pekua near Cox's Bazar, which can host multiple submarines.

This evolving landscape threatens Indian coastal security and stresses the importance of enhanced surveillance and countermeasures against potential adversarial anti-India maritime actions.

India’s nuclear submarine program also includes the development of next-generation platforms. The S-4-class SSBNs (ballistic missile submarines) are larger and more capable than earlier designs, with a displacement of around 7,000 tons and carrying a greater payload of long-range nuclear-tipped ballistic missiles. Alongside these, India is pursuing SSNs (nuclear-powered attack submarines) focused on locating and neutralising enemy vessels, complementing the strategic deterrence role of SSBNs.

SSBNs serve as the sea-based leg of the nuclear triad, engineered for stealthy, long-range second-strike deterrence by remaining submerged for long periods. SSNs, on the other hand, are more versatile, carrying out anti-submarine warfare, intelligence collection, and offensive missions. This dual-submarine approach improves India’s maritime defence, maximising strategic flexibility against various threats.

India’s most ambitious submarine project yet is the S-5-class ballistic missile submarine, with design work reportedly nearing completion and construction aiming to start by late 2027. At 13,500 tons submerged displacement — nearly twice the size of Aridhaman — the S-5 promises enhanced stealth, endurance, and firepower capability tailored for regional Indo-Pacific security challenges.

Anticipated to join the fleet by 2036, this vessel will further solidify India’s credible minimum deterrence posture in the face of expanding maritime threats, particularly from China’s substantial diesel and nuclear submarine numbers.

The Indian Ocean's strategic importance as a global trade artery makes it a rising maritime power contest zone. Nuclear submarines significantly boost surveillance and strike capabilities in this region, crucial for securing sea lanes and protecting economic interests.

As a resident naval power, India faces the strategic imperative to enhance its naval strength and technology to counterbalance rival advances effectively. This effort is vital not just for national security but also for regional stability in one of the world's most significant maritime domains.

IDN (With Agency Inputs)