The Indian 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 a continuous at-sea deterrence (CASD) or follow the Russian-originated Bastion strategy? Besides, who will maintain control over these submarines: the Indian Navy or the Strategic Force Command (SFC) & how does this affect the deterrence equation vis-à-vis Pakistan?
Currently, India has three operational SSBNs: INS Arihant, Arighat, and Ardhiman, with the fourth, INS Arisudan, set to join the fleet in 2027. After completing four Arihant-class boats, India would move on to the next phase of its SSBN program, building the S5-class submarines. However, 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 sub-surface vessels, and both fixed and rotary 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 (US), the United Kingdom, and France, requires maintaining at least one fully armed SSBN on deterrent patrol round the clock. To ensure that, a country requires a fleet of at least three SSBNs to pursue a CASD posture; one on patrol and the remaining two in transit or maintenance.
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. This was based on four key premises: it allowed the Indian Navy to safeguard its SSBN fleet from adversaries’ anti-submarine warfare (ASW) platforms. Secondly, less than a decade ago, India had only INS Arihant, which was more of a technological demonstrator than an active deterrent platform, rendering it highly unlikely that the sub carried nuclear payloads during peacetime. Thirdly, the Indian Navy did not have a submarine docking facility for replenishment purposes (food/medical evacuation) other than its naval bases along the Indian shoreline.
However, developments over the last few years indicate that New Delhi has already decided to operationalize the CASD posture. This is evident from several tangible aspects. 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 now has an additional facility, an operational jetty at Agalega Island in the Western Indian Ocean, which can be used to replenish SSBNs but not to load SLBMs. This will provide an additional haven for SSBNs because the adversary cannot focus solely on the Bay of Bengal to hunt Indian SSBNs. Also, the latest report released by the Stockholm Institute of Peace and Research Institute (SIPRI) has 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.
Deploying SSBNs with nuclear weapons onboard is not significant, but a key aspect pertains to their 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, command of the submarine during deterrent patrol, and, finally, the authorization to launch the nuclear payload will remain with the SFC, which operates under the aegis of the Nuclear Command Authority (NCA).
India’s evolving SSBN posture confirms the deployment of nuclear warheads on SSBNs. 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, the expanding fleet of India’s SSBNs and the deployment of nuclear warheads on them mark the beginning of a new but distinct challenging phase, in which New Delhi will have an edge over Islamabad because the former 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 along with the deployment of nuclear weapons on them, 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. Besides, Pakistan 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. These measures are important because 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 unprovoked military strikes against Pakistan. Keeping this in view and the Indian growing aspirations to have an impenetrable missile defense along with an operational sea-based nuclear force, a possibility exists that New Delhi may resort to launch first strike in a crisis situation. Therefore, it is imperative for Pakistan to take appropriate measures as mentioned above to not only reduce India’s first strike contemplations but to maintain Mutually Assured Destruction in the region.
This article was published by The Diplomat in another form at https://thediplomat.com/2026/07/indias-expanding-ssbn-force-and-what-it-means-for-pakistan/
Abdul Moiz Khan is Research Officer at the Center for International Strategic Studies (CISS), Islamabad.
