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 posture.
The next question regarding India’s SSBN program relates to operational control. The Navy and the SFC both retain control of the SSBN fleet within their respective domains. As far as day-to-day operations, crew selection, and maintenance are concerned, the command remains with the Navy. However, when it comes to the custody of nuclear warheads, their mating with SLBMs, loading and offloading, and command of the submarine during deterrent patrols, those tasks are the remit of the SFC. Perhaps most importantly, the authorization to launch the nuclear payload will remain with the SFC, which operates under the aegis of the Nuclear Command Authority.
India’s evolving SSBN posture confirms the deployment of nuclear warheads on these submarines. This should not come as a surprise because its land-based missiles, such as Agni-P, are already encapsulated in a canister, integrating both the warhead mated and the delivery system. According to SIPRI, only 12 warheads are deployed, indicating that SLBMs from only one SSBN are mated with nuclear warheads. However, soon, remaining submarines will be equipped with nuclear warheads as well. Moreover, signaling from the Indian side confirms the enhanced role of maritime assets in future operations, both conventional and nuclear.
For Pakistan, India’s expanding fleet SSBNs and the deployment of nuclear warheads on them mark the beginning of a new but distinctly challenging phase. New Delhi will have an edge over Islamabad because Pakistan does not possess an operational SSBN and has not yet initiated construction of one. Moreover, Indian advancement in the SSBN domain cannot be seen in isolation. It should be analyzed as part of India’s broader nuclear strategy not only to attain the capability to launch swift strikes from both land and sea but also to absorb the opponent’s retaliation. India’s Mission Sudarshan Chakra, an ambitious effort to intercept incoming airborne projectiles, is part of that effort.
As India’s second-strike capability is increasing with the expanding fleet of Arihant-class SSBNs, now confirmed to carry nuclear weapons, Pakistan has to pursue the development and deployment of its own SSBN force. This will remain under the strict cardinal principles of Pakistan’s Full Spectrum Deterrence response, which is grounded in the notion of credible minimum deterrence. Pakistan also has to accelerate the hardening of its land-based nuclear facilities and pursue a dispersal strategy.
In the meantime, Islamabad should continue to invest in augmenting its intelligence, surveillance, and reconnaissance capabilities by launching additional satellites into orbit to monitor Indian strategic assets. This is extremely important because battlefield transparency will be a key deterrent force multiplier in future conflicts.
India’s belligerence has increased in the last few years, as evident from the actions taken by the Indian side in 2019 and 2025 respectively, when it launched military strikes against Pakistan. Keeping this in view along with India’s growing aspirations to have both impenetrable missile defense and an operational sea-based nuclear force, the possibility exists that New Delhi may resort to launching a first strike in a crisis situation. Therefore, it is imperative for Pakistan to take appropriate measures, not only to reduce India’s first strike contemplations but to maintain mutually assured destruction in the region.
