India's Undersea Nuclear Strategy: Navigating Between CASD and Bastion Approaches

**India's Growing Undersea Nuclear Deterrent: A Strategic Shift** India's pursuit of enhancing its nuclear deterrence is markedly underscored by the expanding capabilities of its Arihant-class submarines. The commissioning of INS Arihant in 2016 represented a significant milestone, and as New Delhi prepares to bring additional submarines into service, it raises vital questions about the overarching strategy guiding this program. Will India lean towards continuous at-sea deterrence (CASD), a posture that emphasizes maintaining an armed submarine at sea at all times, or will it adopt the more static bastion strategy, which confines these submarines within well-defended coastal areas? Moreover, the issue of command structure remains contentious: should the Indian Navy or the Strategic Forces Command (SFC) take precedence in this pivotal role? With three operational SSBNs—INS Arihant, Arighaat, and Aridhaman—and the anticipated addition of INS Arisudan by 2027, the question of which strategic approach India adopts becomes increasingly pressing. The bastion strategy, a concept pioneered by the Soviet Union, involves positioning submarines in protected maritime zones near one's shores, fortified against potential attacks. This method poses significant challenges for adversaries seeking to neutralize such assets. In contrast, CASD entails a persistent deployment of an SSBN, a demanding requirement that necessitates a fleet of at least three submarines—one on patrol, with the others in transit or maintenance. Less than a decade ago, it seemed reasonable to assume that India would adopt the bastion approach, particularly given that the Arihant was largely viewed as a technological demonstration rather than an operational deterrent. The absence of a capable docking facility further limited its strategic maneuverability, confining operations to the Indian coastline. Yet, recent developments suggest a pronounced shift towards CASD. By 2027, India is poised to have a fleet of four operational SSBNs, fundamentally altering its deterrence dynamics. This shift is further facilitated by new facilities, such as the operational jetty on Agalega Island in Mauritius. This new location allows for replenishment operations, thereby extending the operational range of India’s SSBNs beyond the Bay of Bengal. Furthermore, a recent report from the Stockholm Institute of Peace Research (SIPRI) indicates that India has already deployed a limited number of nuclear warheads on its submarines, validating the existence of at least one submarine engaged in a constant deterrent patrol—a clear affirmation of the CASD posture. Operational control over these submarines remains a complex matter. While the Indian Navy oversees daily functions—such as crew management and routine maintenance—the discharge of nuclear armaments and operational command fall under the jurisdiction of the SFC. This bifurcation raises critical questions regarding accountability and response timelines should a crisis emerge. As the capabilities of India’s SSBNs evolve, they signal a broader strategic intent that goes beyond mere deterrence. The integration of nuclear payloads on underwater platforms parallels advancements in its ground-based missile systems, such as the canister-ready Agni-P. Though currently limited to around 12 deployed warheads, expanding this arsenal will likely become a priority as India seeks to solidify its maritime nuclear capabilities. For Pakistan, the implications are stark. The emergence of India's robust SSBN fleet disrupts the existing regional balance, forcing Islamabad to consider the development of its own undersea deterrent. This development is crucial to sustain what Pakistan views as a minimum credible deterrent against a more militarily progressive neighbor. In response, Islamabad must not only accelerate its strategies for land-based deterrence but also strengthen its intelligence-gathering capabilities to effectively track Indian naval movements. As the stakes rise, with India showcasing assertive military strategies, the potential for escalation adds a layer of urgency. Whether through the risk of a first strike or a miscalculation in a heightened crisis, Pakistan's need for a comprehensive approach to deterrence has never been more pressing. The evolving security paradigm emphasizes the need for strategic equilibrium that ensures future regional stability hangs on a delicate balance of power.

A Shifting Balance of Power

The dynamics between India and Pakistan are entering a precarious new chapter, driven largely by India's ongoing expansion of its nuclear submarine fleet. With the addition of nuclear weapons to its submarines, India holds a significant advantage over Pakistan, which currently lacks its own operational submarine-launched ballistic nuclear capability. This asymmetry not only veers the strategic balance but also raises the stakes for Islamabad, compelling it to rethink its deterrence strategy. What’s particularly striking is how India's advancements in underwater nuclear capabilities coincide with broader ambitions encompassing quicker strikes and improved defensive measures. The Indian initiative, known as Mission Sudarshan Chakra, aims to develop a robust missile defense system—one that might bolster its confidence in engaging more assertively. Yet, this isn't just about capability; it’s about the perception of power and the frightening potential for miscalculation, especially if India feels emboldened to act with greater decisiveness.

The Implications for Pakistan

In light of these developments, Pakistan finds itself in a challenging position. With India's second-strike capability gaining momentum through the Arihant-class SSBNs, Islamabad will likely need to accelerate its efforts in developing a counterforce of its own. The pursuit under the principle of credible minimum deterrence will require not only building an SSBN program but also intensifying efforts to secure and harden its existing land-based nuclear facilities. Moreover, intelligence, surveillance, and reconnaissance (ISR) are becoming non-negotiable elements of Pakistan’s strategy. Investing in satellite capabilities could provide much-needed oversight of Indian military movements, serving as a vital tool to counter any advantages that the latter may acquire. Transparency on the battlefield will play a crucial role as tensions escalate.

Heightened Tensions Ahead

India's increasingly belligerent posture, highlighted by its military actions in 2019 and 2025, indicates a readiness to assert itself— a mindset that could lead to a grave miscalculation in times of crisis. The combination of missile defenses and a sea-based nuclear arsenal might tempt the Modi government into contemplating first-strike options, a perilous possibility for regional stability. To navigate these treacherous waters, Pakistan must prioritize measures that not only deter India from such provocative actions but also ensure a balance that favors mutual assured destruction. This precarious strategic equilibrium is not merely about military assets; it’s about maintaining a tense peace that resists the seductive pull of first strikes from either side. As analysts and policymakers monitor this evolving situation, one thing is clear: the increasingly complex interplay between India's expanding nuclear capabilities and Pakistan's response strategies will define the contours of South Asian security for years to come.