How conventional submarines are redefining the strategic balance in the IOR

Junaid Suhais

Navalists of the Cold War era argued, with considerable justification, that nuclear submarines were the decisive undersea instruments. They offered unlimited endurance, high transit speeds, and the ability to operate in any ocean without the exposure risk of a snort cycle (snorkeling). The logical corollary was that conventional submarines, however sophisticated, were relegated to the littoral, the choke point, and the defended anchorage. They were tactical instruments in a strategic competition dominated by the SSN.

That framing was constructed for specific strategic geography: the North Atlantic and the Western Pacific, where ranges were vast, transit corridors predictable, and the operational premium on high-speed passage was acute. It was never an accurate description of the Indian Ocean.

The Indian Ocean is not the Atlantic. It is a semi-enclosed basin bounded at its northern terminus by the Indian subcontinent, shaped at its western approaches by the Arabian Peninsula and the Horn of Africa, and punctuated at its eastern exits by the archipelagic chokepoints of the Indonesian archipelago. The consequence of this geography is that the ocean’s principal strategic corridors compress into narrow transits of acute tactical significance: the Strait of Hormuz, through which roughly 21 million barrels of petroleum flow daily; the Bab-el-Mandeb, through which approximately 6.2 million barrels move each day; the Strait of Malacca, transited by an estimated 90,000 vessels annually; and the Sunda and Lombok Straits, which offer alternative passages but impose their own geographic and acoustic constraints.

These chokepoints share three characteristics that render them extraordinarily hospitable to conventional submarine operations. First, they impose depth constraints. The Strait of Hormuz averages between 35 and 90 metres in its navigable channels. The Bab-el-Mandeb’s main channel rarely exceeds 100 metres. At such depths, nuclear submarines sacrifice many of their acoustic and manoeuvring advantages while conventional submarines, optimised for littoral operations, operate within their designed performance envelope. Second, they concentrate traffic into predictable corridors, reducing the area-search problem that makes open-ocean interception operationally demanding. Third, the acoustic environment in high-traffic, shallow-water straits is inherently complex: propeller cavitation from commercial shipping, biological noise, salinity gradients, and thermal layering collectively degrade passive sonar performance and extend the detection ranges that a competent SSK crew requires to survive.

The strategic implication is both simple and consequential. In the Indian Ocean, geography does not merely favour conventional submarines as coastal defenders. It makes them instruments capable of threatening the seaborne commerce upon which every regional economy depends, of interdicting naval force movements through critical transits, and of imposing disproportionate costs on adversaries with expensive, deep-water-optimised Anti-Submarine Warfare (ASW) assets. The ocean’s geometry is a force multiplier for the SSK.

INDIGENOUS MILESTONE An illustration showcasing DRDO’s AIP system

This is not a theoretical proposition. China’s People’s Liberation Army Navy (PLAN) has recognised it. Pakistan’s Navy is operationalising it. Iran’s submarine doctrine is built around it. The strategic question for India is whether its force structure and procurement trajectory are calibrated to operate effectively in the same geometry, or whether institutional inertia and programme delay are ceding the undersea competition before the contest has fully formed.

Indian Ocean & the SSK

The conventional wisdom that nuclear submarines are intrinsically superior to conventional submarines requires systematic interrogation before it can be applied to Indian Ocean operational scenarios. The SSN’s advantages are real but not universal, and they diminish substantially in the environments that define Indian Ocean competition.

Endurance without indiscretion: The SSN’s primary operational advantage is genuinely unlimited submerged endurance. A conventional submarine must periodically raise its snorkel mast to run diesel generators, creating a detectable acoustic and electromagnetic signature. In open-ocean environments with capable adversarial ASW patrols, the indiscretion rate of a snorting SSK constitutes a measurable threat to its survivability. In the congested chokepoints and littoral approaches of the Indian Ocean, however, the acoustic environment is sufficiently complex that a well-managed snort cycle in high-traffic waters represents an operationally manageable risk. The threat calculus changes when the ocean itself provides acoustic cover.

Speed and transit time: The SSN’s high submerged sprint speed is decisive for oceanic transit—repositioning from the Atlantic to the Indian Ocean or racing to support a carrier strike group. In the Indian Ocean’s confined strategic corridors, however, sprint speed confers diminishing operational returns. A submarine positioned in the Malacca approaches, or the western Arabian Sea, does not require 25-knot submerged transits to execute its mission. It requires persistence, quieting, and endurance at patrol speed. At three to five knots, a modern fuel-cell Air Independent Propulsion (AIP) submarine is acoustically indistinguishable from the ambient noise floor of the surrounding ocean in most Indian Ocean environments, as noted in US Naval Institute (USNI) Proceedings analysis of AIP operational implications.

Cost and numbers: This may be the most strategically decisive variable. A Virginia-class SSN costs approximately USD 3.4 billion per hull. A modern AIP-equipped SSK, depending on specification, ranges between USD 400 million and USD 1.2 billion. The cost differential of three to eight times means that a navy with a fixed capital budget can field three to eight conventional submarines for every nuclear attack boat. In a contested littoral environment where multiple simultaneous commitments are the operational baseline, mass matters. India’s strategic requirement is not to win a single engagement against a peer SSN in open water. It is to sustain credible underwater presence across the Arabian Sea, the Bay of Bengal, and the Andaman Sea simultaneously, while maintaining sufficient operational reserve for surge deployments and refit cycles. No credible fiscal projection supports meeting that requirement exclusively with nuclear attack submarines within the relevant planning horizon.

The Pacific comparison: The contrast with the Western Pacific is analytically instructive. In the Pacific’s vast oceanic distances, the SSN’s speed, endurance, and deep-water performance advantages are genuinely decisive. The US Navy’s decision to operate no conventional submarines reflects the operational demands of that specific theatre. The AUKUS agreement, which will provide Australia with Virginia-class SSNs rather than advanced SSKs, similarly reflects a strategic judgement about Pacific range and endurance requirements. Applying the same logic to the Indian Ocean is a category error. The geography is different, the operational requirements differ, and the acoustic environments differ. SSKs operating in their designed envelope in the Indian Ocean are not a second-rate substitute for SSNs; they are often a better fit for the specific operational demands of the region.

The Endurance Revolution

The technological evolution of the conventional submarine over the past three decades constitutes one of the most significant and underappreciated developments in contemporary naval warfare. It has not, as some enthusiastic commentary suggests, eliminated the gap between SSK and SSN performance. It has, however, shifted the operational threshold at which that gap becomes strategically decisive.