Continuous at sea deterrence — India's gamble in Indian ocean

India's evolving strategic posture in the Indian Ocean is increasingly shaped by Continuous at Sea Deterrence, which seeks to ensure the permanent deployment of at least one nuclear-armed ballistic missile submarine (SSBN) for an assured second-strike capability. While India promotes this development as part of "credible minimum deterrence", the expansion of its nuclear capabilities suggests a shift toward a more assertive and potentially escalatory counterforce posture. This transformation has significant implications for global strategic stability within the complex security matrix of South Asia.

India's SSBN programme was formally launched under the ATV project, with collaboration between the Indian Navy, the Bhabha Atomic Research Centre, and the Defence Research and Development Organisation. The commissioning of INS Arihant in 2016 and its first operational patrol in 2018 marked India's entry into the exclusive club of nuclear triad powers. Since then, the programme has accelerated rapidly. INS Arighat was commissioned in August 2024, and the S4 and S4* SSBNs are undergoing sea trials with operational status expected by 2025-26. Additionally, India is developing a new S5-class, expected to displace 13,500 tons, signaling the shift to a more survivable and capable platform.

These submarines are being paired with India's K-series submarine-launched ballistic missiles (SLBMs). While the K-15 (750-1,500 km) is already in service, the K-4 (3,500-4,000 km) has been tested and is nearing deployment. Furthermore, the K-5 SLBM, reportedly has a range exceeding 5,000 km and equipped with Multiple Independently Targetable Reentry Vehicles (MIRVs), followed by the K-6 hypersonic missile with 8,000 km range, which is under development. These MIRV-capable SLBMs would enhance India's capacity to strike from relatively secure maritime bastions.

India's strategic thinking draws inspiration from historical precedents, notably the bastion strategy of the former Soviet Union. The Soviets deployed their SSBNs in heavily fortified maritime zones to shield them from enemy attacks. India appears to be adapting this strategy in the Bay of Bengal. Iskander Rehman in Murky Waters: Naval Nuclear Dynamics in the Indian Ocean notes that this geography allows Indian SSBNs to maneuver with greater stealth compared to the congested Arabian Sea. In line with this approach, Project Varsha, an underground submarine base under development, would further strengthen India's ability to sustain continuous deterrence.

However, India's technical and operational challenges also expose critical vulnerabilities. Tony H. An at the Naval Postgraduate School in Monterey, notes that INS Arihant was originally designed as a nuclear-powered attack submarine (SSN) and only later modified to carry ballistic missiles, a structural retrofit that compromises the hydrodynamic and acoustic qualities necessary for an effective SSBN. These shortcomings were illustrated when INS Arihant was rendered inoperative for ten months after seawater flooded its propulsion system, highlighting how human error and design compromises can jeopardize a platform intended to deliver the most destructive weapons.

According to former Indian Navy Commodore Anil Jai Singh, "One submarine always needs to be on patrol. If Arihant is in and out of the harbor, it is not exactly a deterrent. We need 3 to 4 SSBNs so we can keep one on patrol, when one may be in port, one going for patrol, and one coming back." However, concerns remain about India's ability to achieve such reliability, given recurring issues in serviceability, training and maintenance. Furthermore, India's sea-based deterrent introduces challenges to command and control. Unlike land-based missiles which remain under centralised civilian oversight, SSBNs operate in a domain where instant communication is inherently challenging.

During the Cold War, both the US and Soviet Union experimented with different mechanisms, ranging from pre-delegation of launch authority to electro-mechanical locks on missiles to balance survivability with civilian control. In India's case, it remains unclear how launch authority will be managed. Vipin Narang and Yogesh Joshi suggest that India's "canisterized" SLBMs may require pre-delegation to naval commanders. If that is the case, this would raise significant concerns about the erosion of civilian oversight and the increased risk of accidental or unauthorised launch.

In maritime environments, where rival submarine forces operate in close proximity of each other and communication is limited, it becomes difficult to determine whether a submarine is armed with a conventional or nuclear warhead. This ambiguity is particularly dangerous during periods of heightened tensions. For instance, the mere presence of an Indian naval platform with dual-capable missiles could be perceived as a nuclear signal, potentially prompting preemptive or escalatory measures. These risks are underscored by the 2019 Pulwama-Balakot crisis, during which India reportedly deployed a SSBN alongside its aircraft carrier battle group, demonstrating a willingness to rely on strategic assets even at low thresholds of escalation.

India's projected plan to field a fleet of 10 to 12 nuclear-powered submarines, comprising SSBNs under the Arihant-class programme and SSNs under Project 75-Alpha, allegedly in response to the "China-Pakistan threat", would likely fuel an arms race in South Asia. Regional states may respond by acquiring more advanced anti-submarine warfare capabilities or by pursuing their own nuclear options, thereby complicating the deterrence equation. These dynamics raise the possibility of inadvertent encounters at sea, which without robust communication mechanisms could escalate into nuclear crises.

Historically, the US and former Soviet Union sought to reduce such risks through maritime confidence-building measures, including the 1971 Agreement on Measures to Reduce the Risk of Outbreak of Nuclear War and the 1972 Incidents at Sea Agreement. In South Asia, Pakistan and India signed an Agreement on Advance Notice of Military Exercises in 1991, and committed under the Lahore Declaration in 1998 to conclude a pact to prevent naval incidents. However, little progress has been made. Incidents such as the 2011 encounter between INS Godavari and PNS Babur underscore how quickly miscalculations can spiral into strategic crises, in the absence of dedicated hotlines or protocols to de-escalate conflict between navies.

India's increasing reliance on sea-based nuclear assets brings with it a host of operational risks and strategic uncertainties. These are amplified by the lack of transparency in India's nuclear command and control, exemplified by the March 2022 so-called "accidental firing" of BrahMos nuclear capable supersonic missile into Pakistan, the technical vulnerabilities of its SSBN fleet, and the region's fragile political environment. In the long term, unless India clarifies its doctrine, adopts robust safety mechanisms and engages in nuclear risk-reduction diplomacy, the very platforms meant to ensure strategic stability could become triggers for conflict.