Asia Defense | Security | South Asia

India’s Expanding SSBN Force and What It Means for Pakistan

As India’s expanding fleet of Arihant-class subs improves its second-strike capability, Islamabad has to pursue the development and deployment of its own SSBN force.

India’s nuclear-powered ballistic missile submarine (SSBN) program has come a long way since the commissioning of INS Arihant in 2016. This brings a few key questions into the spotlight: Will India pursue continuous at-sea deterrence (CASD) or follow the Russian-originated bastion strategy? Who will maintain control over these submarines: the Indian Navy or the Strategic Forces Command (SFC)? And how does the growth of India’s SSBN count affect the deterrence equation vis-à-vis Pakistan? 

Currently, India has three operational SSBNs – INS Arihant, Arighaat, and Aridhaman – with a fourth, INS Arisudan, set to join the fleet in 2027. After completing four Arihant-class boats, India will move on to the next phase of its SSBN program, building the S5-class submarines. These developments raise an important question: which strategy would India adopt for its SSBN force in the immediate future? 

The bastion concept, pioneered by the Soviet Navy, advocates deploying the SSBN fleet within a heavily defended maritime zone near one’s shores, rather than dispersing SSBNs widely across the open ocean. The maritime zone is protected by surface and subsurface vessels, as well as both fixed and rotary anti-submarine warfare (ASW) platforms, making it extremely challenging for the adversary to sink them. 

On the other hand, the CASD posture, historically associated with the United States, the United Kingdom, and France, requires maintaining at least one fully armed SSBN on deterrent patrol round the clock. A country needs a fleet of at least three SSBNs to pursue a CASD posture; one on patrol and the remaining two in transit or maintenance. 

At first, it was widely assumed that India would adopt the bastion strategy and keep its SSBN fleet in the Bay of Bengal, closer to its shores. That would allow the Indian Navy to safeguard its SSBN fleet from adversaries’ ASW platforms. This seemed like a likely strategy less than a decade ago, when India had only one SSBN, the INS Arihant. The Arihant more of a technological demonstrator than an active deterrent platform, rendering it highly unlikely that the sub carried nuclear payloads during peacetime. In addition, the Indian Navy did not have a submarine docking facility for replenishment purposes other than its naval bases along the Indian shoreline. This meant its SSBNs were restricted in range.  

However, developments over the last few years suggest that New Delhi has already decided to operationalize the CASD posture. To begin with, India will have four operational SSBNs by the end of 2027, allowing New Delhi to deploy at least one submarine at sea 365 days a year. With four operational SSBNs, India can maintain a realistic patrol rotation: one boat on active deterrence patrol, one in transit or worked up for patrol, one in maintenance and refit, and one undergoing training cycles or weapons qualification. 

India also has an additional facility, an operational jetty at Mauritius’ Agalega Island in the Western Indian Ocean, which can be used to replenish SSBNs, but not to load submarine-launched ballistic missiles (SLBMs). Since the facility was inaugurated in February 2024, India’s adversaries cannot focus solely on the Bay of Bengal to hunt Indian SSBNs. 

Finally, the latest report released by the Stockholm Institute of Peace and Research Institute (SIPRI) revealed that India has deployed a limited number of nuclear warheads onboard its SSBNs. This indicates that New Delhi already has one SSBN on constant patrol, equipped with nuclear-tipped SLBMs, thereby confirming the adoption of the CASD........

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